Cheers for that. It was exactly the answer i was looking for. I could be wrong but im guessing the focusrite isa one would probably have slightly better preamps since its a specific product for that.
Yes and no. Up to a point, you can sometimes say that yes, one preamp is better than another, especially when comparing cheap 'prosumer' gear like m-audio for example to something more respectable. But when there are quality components involved, it's never a simple matter of saying one is better than the other. For a start, different preamps interact differently with different mics, and then going beyond that, different combinations of mics and pres deliver different colour depending on the source material. So, once you're using quality gear, it really comes down to horses for courses. You might find that the Duet's preamp sound, combined with a certain mic you use, gets you a sound you prefer with say, a certain vocalist's timbre. Or in other cases, the focusrite might give you something nicer.
This is why you find dozens of different preamps in the biggest studios.. if it were the case that one was just better than all the others, then logically they'd only have the best most expensive one.