Agreed, the D4 USB DAC is better than the D3, and slightly better than D10 via USB, but if you can use optical the D10 can do native 24/96 hires music files.
Also consider the Pico DAC-only as one of the best USB DAC's out there (USB receiver > I2S > AD1796 ASRC chip to upsample to 24/96 > Wolfson WM8740). And the $99 Nuforce uDAC which is very close in sound but also includes a very nice headphone amp section (USB receiver > I2S > ESS Sabre 9022 DAC with oversampling and DSP jitter reduction but not upsampling).
Both have line out, but the Pico DAC gives you both RCA and 1/8" line-out to connect two amps. The uDAC has RCA line out, or 1/8" headphone out, and only one is active at a time, but it adds S/PDIF coax out as well. They both run off USB power alone, no batteries.
If pressed hard I would say the D4, D10, Pico and uDAC are all close enough to just pick them based on features.