Which DAC is better?

I appreciate your input.
I am looking for a dac unit mainly for the usb port to connect to a computer.
The following brands are in my mind;
Arye QB9, Simaudio Moon 300D or Arcan fmj D33.
In the Arcan brochure they use a super usb so the sound is better. I am illiterate in computer or digital.
Check out the PS Audio PerfectWave DAC MKII.
Gosh, "super USB", well that must be the best...

There's no such thing as super USB.

The Ayre and the Arcam will accept both USB 1.1 and USB 2.0. USB 1.1, otherwise misleadingly known as "full speed" USB, will allow you to run up to 24/96 source material. Above that, it simply will not pass the bandwidth required.

So, to run higher sample rates (e.g., 24/176, 24/192), you need to use the newer USB 2.0 (which permits 40x the data as USB 1.1). The Ayre and the Arcam units support this (although your computer may not), but the Simaudio does not. In fact, the Simaudio states that its USB input will accept ONLY up to 16/48. If you want anything more than that, you need to convert the USB to some other digital format through an offboard converter, and then use that input into the Simaudio. Hence, while the Simaudio provides the capacity to run high def material, it will not accept it over USB....

Otherwise, if it matters, the flexibility of the Arcam and the Simaudio are greater than the Ayre. That is, they both have multiple digital inputs, accepting multiple formats. The Ayre has a single USB only – it is a 100% dedicated, single-purpose USB DAC. Thus, if you want to run anything other than USB, or more than one digital source, the Ayre aint the one for you. Looks like none of them have volume control, if that matters. Also, from the literature, looks like the Simaudio will upsample internally. I know that the Ayre does not, and it looks like the Arcam doesn't either. The Arcam and the Ayre run asynchronous USB, while the Simaudio appears to address jitter through a "proprietary digital clocking system." Asynchronous USB is, by many, considered to be the best option these days. So, the feature set for each is different. The Arcam and the Ayre appear to offer state-of-the-art functionality over USB. The Simaudio does not. In fact, from the technical data, suggests that USB on the Simaudio may have been somewhat of an afterthought.

Sound-wise, that's up to you. Have an Ayre, and it sounds great. But no experience with the other two, so can't really say. There are also many, many other options in that general price range. I suspect that a search regarding USB DACs will give you more suggestions than you could possibly want.
Can comment only on the qb-9. Its a really good dac on its price range, very musical.
If you want to spend maybe less, the DA-160 is a nice option.
Try a Tranquility DAC
Mezmo, thank you for your well known knowledge. I will choose Arcam if the sound quality is same or better than QB9. Do you recommend any other DACs? Also I may have to learn more about digital terminology.
I think all 3 choices are very good. Ayre happens to be my favourite in solid state electronics. Naturally, that would be my first choice. I've also had Arcam CD players. Both products sound great, but they are very different from each other. Arcam digital products are very listenable. They have a refined, polite sound that you can listen to all day. The Ayre is completely different. The sound is very liquid and pure. It has tons of resolution, as well. Some say it is analytical but I would disagree with that. For all its resolution, it is a very musical component. Given the vast difference in sound between them, I would strongly urge you to listen to both before making a decision. I am not that familiar with the Sim but if I had to guess, it would fall somewhere between the other 2.
I own the Simaudio 100D, the little brother of the 300D, and it's a wonderful, natural sounding DAC.

If your primary source will be USB, though, the 300D is probably not the best choice. Simaudio makes it very clear in their description of both the 100D and the 300D that they put their effort into the SPDIF circuits and include the USB input mostly as a convenience.
Yea, the conversion to a computer-based source can be daunting at first, but if you're inclined to keep at it, it will be old hat in no time.

My first-hand experience with different DACs is somewhat limited. Have an Ayre and an MHDT Havana. They are very different animals. The MHDT is a non-oversampling (“NOS”) DAC. That is, it uses cost no object DAC chips from, say, 20 years ago with a USB (and other) inputs. If all of your source material is standard CD (the standard is called “redbook” and is encoded with a 16 bit word length and sampled 44 thousand times per second, which is what 16/44 represents) then a NOS DAC makes some sense. In effect, it’s chips address all redbook material in native resolution because, you guessed it, the best chips from the hey-day of CD ran only 16/44. (Or, at least that’s my imperfect understanding – the Ayre doesn’t “upsample” either, but will run high-rez up to 24/192, while the Havana will not…). But if you want to run any higher-rez material or upsample, one of the DACs running these old-school chips isn’t your answer. Personally, prefer the Ayre, but there are those who don’t. Also liked the Bel Canto, which is actually not a USB DAC, although it does have multiple inputs and a volume control, so can function as a stand-alone preamp as well. To run USB into the Bel Canto, you need a separate Bel Canto converter ($500). Sounds great, and a fine non-asynchronous USB solution. I went with the Ayre.

Otherwise, the original (pioneer, really, I believe) of asynchronous USB is Wavelength Audio. They do multiple iterations of tubed DACs that are meant to be very nice. For years, Wavelength was the only game in town for asynchronous, and everyone else was either working on different technological answers to jitter in an off board DAC, decrying USB DACs as inferior, or waiting it out. Ayre, for it’s part, licensed Wavelength’s asynchronous tech, and thus became the first (and for a spell, I believe only) solid state asynchronous USB DAC on the market. Think it was these two that really opened up the market, and since then there has been a real explosion of asynchronous USB DACs (presumably using iterations of the basic technology to do the same thing). These days, seems that asynchronous is the prevailing way to go with USB to a DAC, but there are many that offer different solutions as well (i.e., the Bel Canto or the Simaudio). Everyone, from “The Names” to newcomers seems to be getting in on the act, so there are lots of options.

As for what’s caught my eye – and admitting that I have no first-hand experience – been interested in the offerings from the likes of Naim, ARC DAC 8, and recently seen some good feedback on the Rotel. The Benchmark DAC-1 is another, and one that seems to be very polarizing (it is from an established pro audio shop that has made a big crossover, and folks seem either to love it or hate it). More recent-ish additions, the offering from Empirical Audio (which is very active on these forums) looks interesting, and a lot of good feedback regarding the Wyred4Sound DACs. I’d love to hear all of these, but haven’t had the chance. So, lots and lots (and many more) to choose from. Best of luck and enjoy.
The new Cambridge Audio Dacmagic "Plus"...the USB works swimmingly...a friend has one, I heard it, it's sweet...my original Dacmagic has a sucky USB system that I don't have a use for so that's fine.
I think by the word super, you meant "asynchronous"

Not all USB interfaces are designed alike. Most are synchronous, with the PC acting as the master clock. As you can imagine, the PC clocks are not the most ideal for for high end digital audio

Asynchronous creates a master clock outside and puts the PC as a slave for sending data. It results in less jitter. Most of the better async USB DACs tout this feature.

And if that's not confusing, enough, not all asynchronous USB interfaces are identical either.

I've had very good results with a Wavelength Wavelink USB interface vs an M2Tech Evo, despite both claiming an async interface.

One of the best USB interfaces I have used is the OffRamp.
Easy, Arye QB9.

Moon DACs are generally excellent - but that's their top of the line stuff. I just can't believe they would make their entry level sound any good.

Arcam should be taken out and shot for using words like "super USB" - I believe that's enough of a reason to avoid that DAC. Just think, a word like "super" has so much potential -- super coax, super Toslink, super FET, super bipolar, super feedback, super balanced, super Ethernet, super transformer. I suppose when a company runs out of design ideas, it could start adding "super" to everything in order to distinguish its mediocre product.
Chesebert - Is your assessment of the Moon DACs based on having heard one?

I have only heard their top of the line 750D (by itself, without comparing to my own or other DACs). I have not heard their entry level, but I can only assume it (I know I shouldn't) to be of significant lesser quality.

Any chance you can audition both DACs? QB9 does require some computer knowledge (non-trivial for high-quality USB sound) - I am sure your ayre dealer will be happy to walk you through setup procedures.
What about the W4S DAC2? a nice contender.
Some corners obviously had to be cut from the 750D to make the 300D (figuratively speaking, as I don't know if they share anything designs-wise). Obviously it won't sound as good, and nor should it. But that doesn't make the 300D or even 100D uncompetitive in their respective price range. IMO Simaudio has always had a great sound quality per dollar ratio, from top to bottom. The presentation may not be everyone's cup of tea, but what is?

Simaudio is easily worth considering. I liked the Rega DAC more, and for a bit less money, but the Simaudio DAC is easily an excellent piece of gear that should be auditioned if you have a dealer reasonably close IMO.
Having heard the extraordinarily good audio quality of 24 bit material on the Arcam FMJ D33, and given that the Sim Audio does not support 24 bit, then my cash would go on the D33.
Better... they're DIFFERENT, but only your ears can really decided what is better...

Personally, I would say the MHDT Havana is better, but that's because I love the way it sounds. Non-oversampling, tube output, etc.
829yn, I have never heard any of the dacs you list and feel that even USB2 is short of SP Dif and certainly short of FW. As Audiojan says only you can make the judgment. Digital is moving ahead so rapidly, that anything you buy today will be obsolete tomorrow.

I am presently using an Exemplar Audio tube dac that is better than my old Weiss Dac202, but soon I will be getting a FW input dac that runs in native DSD. But it really is a pro dac from Empirical Audio Legacy.
I don't know if I agree that "digital is moving so rapidly that anything you buy today will be obsolete tomorrow"... Computer audio (Hi-Rez) and streaming is moving along pretty quick, but except for that.. not that much is happening. And what is happening is not always for the better. Higher sample rates, more circuits, etc. doesn't necessarily make it sound better... different, yes, but not always better...

I just took a major step backwards in technology... Non-oversampling DAC based upon a chip that is really old, no op-amps, but a tube output instead... And the sound is better than I've ever heard from any digital!
I like your thinking, can you share with us the name of the "old school" dac you chose?