I like the Aardvark too, but be aware -- each outside interface requires a PCI slot in the computer. Up to 4 can be put in any one computer *if* you have the available slots.
The DirectPro has the advantage of having DSP effects (EQ, compression, and reverb) built in. Not good enough effects to use in the final CD usually, but defineatly good enough for what the artist hears in the headphones while recording. Most singers I've worked with like having a bit of reverb on their voice, while I like to lay down the track dry - this lets you do both at the same time easily with NO latency problems.
The DirectPro is 4 channel, the Q10 is 8 - one small note, the Q10 only has phantom power on the first 4 channels.
Of course, you can also mix and match - so if you got the DirectPro now, you can add the Q10 later and have 12 channels of quality sound that are happy to work together.
-lee-