well, one vote here for the UF8-- honestly, it's not even very close, i immediately did not like the feel of the m-audio keyboard-anyone who is looking for a realistic piano feel probably will not be satisfied by the keystation--I'm sure it does fine, however, for what it is-- the UF8, on the other hand, is a real instrument, and i am extremely happy with my purchase even 8 months later--
my advice to u , however, is to go try them out for yourself if that is possible--it's really the only way for u to know what u like-- (maybe if what u r used to is a keyboard feel u might actually prefer the feel of the m-audio)
I just picked up the UF6 and it's semi-weighted keyboard also has a nice feel to it. It's quite a step up as far as features and keyboard quality from the Radium 61. I found it works best using MIDI out and not the USB connection, at least with a Mac and stand alone instruments.
I played the Keystation Pro 88 at the music store when they first came out and didn't care for the action. I have a Yamaha CLP-555 for realistic piano action.
The CME controllers are pretty heavy so invest in a sturdy, stable stand for them. The music store's UF8 stand collapsed while I was there.