That is 3 totally different balls.  Look at it this way:

UFO - nano solid, big core, early snowtire
Physix - nano hybrid, big core, not as early, more angle
Omega Crux - sanded pearl, big core, ever later and more angle....

I find the UFO to be unusable on most conditions except the highest volume of oil or hard surface. 

The Physix would get my vote.  It's the workhorse of my bag and gives me a good indication what's on the lane.

You may want to check out the Halo Vision also. - its a hybrid without the nano load.  It handles the same volumes as the Physix with a later roll and recovery.  They are a great 1-2 punch for me.

Physix, or Crux; From a shape standpoint, without question the case can be made for the Crux. ( Code x, and Physix, both turn hard at the end of the pattern, where the Crux is earlier, smoother, and more continuous than both.

Good luck with your choice.