From all the comments I've heard recently (SPDIF is better! USB is better! AES3 is better!), this seems to be quite system-specific; so, you'll just have to try and see what you like. I like USB myself, not for sound specifically, but because the DAC sets the timing, rather than locking onto a clock sent with the data.
Modern DACs are better at jitter rejection and and less sensitive to USB noise than a few years ago. Let us know what you find out!