The absolute "best" filter/conditioner for digital

Have you tried combinations of approaches?
I don't know about "absolute," but the best I have used is the Pure Power + (for either digital or analog).
I use a PS Audio P600 with the optional board inside. So I can set the A/C output to any frequency from the standard 60Hz up to 120Hz.
Currently I have the P600 set to output 110HzA/C power and use it exclusively for all my digital components.*

*(except for a Behringer DEQ2496 which is not happy with a 110HZ AC in to it's digital power supply, so for that one item I use a standard 60hz AC.)

My digital stuff is happier sounding with the 110 Hz Ac sine wave.

PS: the PS Audio P600 and P1000 MUST have the optional board installed to be able to change the frequency. that board is no longer available. So for those looking to play with this idea... No other regenerators i know of can alter the frequency with a push of a button. So if you want one to do this, remember it HAS to have the optional board installed already.

Personally I would think PS Audio should make a new conditioner with this feature, as it is a killer ap. many folks do not understand.

I first read about the PS Audio P600 doing this mentioned in passing in an article in Stereophile.
I was smitten, and sought out the device.. and was happy to find it's properties to be useful.
Upping the AC hz smooths out the ripple in power supplies and allows more power to be available in the unit so treated.
Foundation Research LC-1
If you want something inexpensive Emotiva has a nice RFI filter with 6 outlets for about $120. Works very good in my system. They also have a two outlet for $99 for power amps. It does not seem to harm dynamics at all and it also besides filtering correct for DC offset in the power line
The difficult thing about power products is that, while 2 people can have the exact same system, they don't have the same electricity. What works for one person may not work for someone else. If you are looking to buy something, I would call The Cable Company. They will send you anything you want to try so you don't get stuck with something that doesn't work for you. I've been using them for years and wouldn't consider doing it any other way.
I agree with Zd542 about trying things out, but in lieu of other information, such as your budget and what you're trying to accomplish, I always recommend the "first do no harm" approach of Shunyata. They have something for just about every budget and their gear has maintained incredible re-sale value over the years...which should tell you something.
Zd542's advice is spot on, but The cable company doesn't carry everything out there. Because of the unique interaction of your electricity with your system, no one can tell you what the best will be, and you could easily blow your whole 401K balance running the experiment. Sadly, finding the best is like winning the lottery, but finding something that works really well is not so hard. In addition to the Cable Company, talk to Chris at VH audio. The guy is a real straight shooter.

I came late to the power treatment party and have been astonished at what it offers.
Dedicated line(s) 1st.
PI Audio Uber BUSS.
Zd542 is right on the money. The Cable Co. may not carry everything (who does?), but they carry Pure Power+, Silver Circle Audio, Shunyata, Audio Magic, Running Springs, Audience and Furutech. The heavy hitters, in other words.
Dedicated lines...most bang for the buck. Otherwise, Audio Magic
Two relatively iconoclastic audio personalities have approached the conditioner question and produced modestly priced products that reliably reduced interference, and subjectively cleaned up, shined up, and polished the sound reproduction in my systems.

Mapleshade's power strips - the stealth power conditioners masquerading as humble power strips. These outdid the benefits of a number of other more expensive "real" conditioners.

Machina Dynamica's provocatively and humorously titled "Flying Saucers" for windows which are tiny, home-made looking trimmed pieces of treated copper which even more dramatically improved the sound reproduction of every audio and video device - even down to the level of tabletop CD boombox!
Important note: At no time was any hallucinatory mushroom ingested.

I venture to guess these are among the most cost effective items to try.
Thanks for the responses!
Thanks again. I particularly like Zd542"s Cable Company info-i will use it. Also,Brownsfan advice will be followed up.
I agree with dedicated lines- but particularly if you isolate them with something like an Equitech or other balanced power transformer or another type of 'isolation transformer'-they strip away and tremendous amount of noise and can be cheap, used or factory blems or transfomers only that you can box and connect yourself, or any electrician. Be sure to buy over your requirements for best advantage. Even if only digital line is isolated the results are amazing. Always looking for new ideas though,transformers are old school but the balanced are current.
Ditto on the Emotiva CMX-6 Common Mode AC Line Filter & Power Distribution System.
AC Power Source:
120 VAC +/- 20% @ 60 Hz; 15 Amps. Load (total for all outlets):
15 amps continuous precision magnetic circuit breaker allows for short-term inrush current of up to 250% of rated load
Power cable: Standard IEC detachable power cord; 7 feet long; 14 AWG x 3
Size: unboxed: 4” wide x 1 3/4” high x 16 3/4” deep
Weight: 3.9 lbs
i use a ps audio dectet as a filter for my transport and dac.

i'm satisfied with the results. however, choose your power cords after a careful comparison of candidates.
Mrtennis I appreciate your power cord advice. It confirms what my experimentation has shown. My Grandfather was a Mariner, and my close cousin is Port Captain in one of the major eastern ports. Mariners say there's a place for everything and out everything in its place. This is probably a good rule for us--it's just to find the perfect place.
I'm laid up after shoulder surgery and will be doing experimentation with what I have when pain is reduced.
These forums have been a great value to me over the years and your input is appreciated :)
I use Monarchy Audios regenerator for my digital and at the cost of a "Good power chord" it wokrs great. I alternate it between my Transport/Dac as well as TT and have found it the best option so far. when used only on digital, on my system it improves the amps performance also and the only reason i could think of was it block some o the digital grunge from getting back into the main power.

If willing to pay more APS used to be great.

I found these to be far better than Filters/conditioners.