USB vs SPDIF, which sounds better?

I am a former Big 7 owner ( previously a Big 6 and an original model 4 as well... ) currently running a Golden Gate. Loved each one for their own best virtues and kept climbing the Lampi ladder... so far, so good. Big 7 is a fantastic dac with outstanding value for the money. I ran a few different S/PDIF’s from my cd transport and USB’s from my Lampi Komputer.. 
Top 3 favorites in no particular order are Mad Scientist, Triode Wire Labs, and WyWires. 
My recommendation for excellence and best bang for the buck is Triode Wire Labs... Pete makes outstanding cables at very reasonable prices... he’ll build anything you need the way you want it... has a 30 day return trial policy and is a real pleasure to deal with. 
If you’re looking for a remarkably natural presentation, I can’t speak highly enough about his products. 
PS: which DHT’s and what rectifier are you running? Just curious...
Good luck and happy lissn’n! Lissnr

I've had an Aurender N10 for a year or two and have tried all of its digital outputs.With that player, they're all pretty good. To my ear, here is the stack rank from best to not-so-best:

XLR: quietest with the biggest soundstage, great midrange & bass,  and most organic sounding (what I use all the time)
SPDIF RCA: very, very close to the above
Optical: not a very deep soundstage, kinda "thin" sounding, but surprisingly good for optical
USB: not as good as any of the others, but OK

I have limited experience with brands of cables and currently run all Shunyata Sigma cables in my primary system save for the speaker cables. I'm sure that there are many good cables out there, but I worked up the Shunyata product line, so haven't tried others. 

@medwardo, thanks for your info.  I recently got a Silnote Poseiden Signature SPDIF RCA cable, and so far I like what I am hearing.  The SPDIF RCA connection does sound fuller, bigger soundstage, and more detail than the USB connection.  I also feel more emotionally engaged to the music than the USB connection.  I may try some more digital cables later on to see how good this can get.

Now using a PS Audio Memory Transport into an upgraded Yiigdrasil SPDIF
Using a WyWires Litespd cable. This cable has a special quality to draw you in to listening. Its the best I have heard in  the last 3 years here on different DACs. Was using the AES connection on the PSMT with a balanced Belden 8402. Very good also.
The Belen killed a DHLabs DH110 which is supposed to be the required 110 ohm
Standard. So, the connection quality varies with equipment used.
The Lifatec optical cable comes close. USB is on the bottom of quality.
Even with all the decrapifiers, been there done that too.