as i wrote in some other post, from my point of view most important for resolume are sliders and knobs! so i would go for a device with loads of them (eg. the UC33). clips can be triggered with the computer keyboard easier than with piano keys anyway...
i personally got myself the PCR50, because i wanted it to use for playing music as well. using it with resolume works really great, but more faders would be better of course.
also make sure to check out the
DOEPFER products like the Pocket Fader & Pocket Dial !
in case u haven' already - there are reviews for most of these controllers @ vjcentral.com!