There's a guy here on the forums who raves about
the UX2, but I think his basis for comparison is non-existant, so take it with a grain of salt. I asked him to post samples to go along with his gushing, but no response. Could be worth a listen if you can get to one.
The DMP3 is almost universally praised for what it is, an inexpensive no frills clean preamp. I have one and love it on acoustic instruments, which I think it does on par with preamps costing many times as much. For vocals, the mojo has to come from the mic with the DMP3, it's just going to provide plenty of clean gain, and very little else. For some, that's exactly what they want, others want "a sound" from their preamp.
I've never heard the Digi 001, so can't help with the comparison. I've used a few Neves, Focusrites, APIs, Tridents, etc., so I do know what a good preamp sounds like. I tend to think less in terms of them being better or worse than each other in the general sense, and more in terms of different and right for a particular application. I would hate to have just one set of all the same pres to record with.
Good luck.