I just purchased an "Oxygen 8 v2" MIDI controler, but I might return it and get an "Axiom 25" instead.
Has anyone used any of these two?

Haven't gotten my hands on an Axiom, but I have played with an original Oxygen8. At a point last year when I needed a compact keyboard with an audio interface, I wound up buying an Edirol PCR-1.

But, if I had it to do over again, and I didn't need the audio interface on the PCR-1, I would seriously have looked at the Axiom. The Axiom has aftertouch and the PCR-1 doesnt. And I've grown to hate the pitch bend on the PCR-1: it's a pressure pad, and it tends to act like an on-off switch -- modulating the pitch bend is very difficult. And the Axiom's finger pads look like they could be handy for tapping out drum parts.

HOWEVER... I've concluded that a two-octave keyboard is just too limiting. You don't need to have much in the way of keyboard chops to grow frustrated with the limitations of always having to change octave settings in order to get through a solo or do anything two-handed. If you like the Axioms, and if you have room in your rig, I'd highly recommend spending the extra seventy bucks and getting the Axiom 49 instead of the 25.