I bought the Fiio D3 because it's $27.00 (I also spent $14.00 on an optical cable to connect it to my mac), and uses the same Wolfson D/A chip as much more expensive DACs from Rega and Cambridge Audio. I'm enjoying the sound immensely, and think it's an improvement over my previous USB DAC (which used the also popular Burr-Brown D/A chip). Whether the improvement is due to the superiority of an optical connection from the computer to the DAC over USB (which is also the DACs power source), the different D/A chip, or a combination of both, I can't tell you. I can tell you 2 things, though:
1. It's hard for me to imagine that a Rega DAC, which costs 44 times as much, sounds even 5 times better. That's something I hope to investigate soon.
2. If you currently connect a computer based digital music source to vintage amplification using the mini headphone out jack on your computer, and your computer has a digital optical or coaxial output, you should buy one of these babies right now.