My past research showed that the Omega was much faster to clean than the Greenstar - as far as juice quality, I feel they're both VERY similar (both excellent). The last time I checked, the Omega had a much longer warranty.
Champions are workhorses, too...there's NO doubt about that. I perceive that the Omega/Greenstar have a *very* slight edge on juice quality (they both run slower/less rpms, hence less heat). However, the Omega can't deal with pineapple quickly or effectively (I resort to the VitaMix to macerate the pineapple, and then "press" the juice) - the Champion (so I've been told) is okay with pineapple. (My next juice feast I'm going to "semi-freeze" the pineapple and see if my Omega can handle that).