Prof x and who else?

witch would be best at making crits. fist would be ok too, although less crits than witch generally. then you have to consider what color you want to tank as the strongest color. even if more covers come in, I'd cap px at 220, so a 166 can take the strongest color instead of px tanking blue as the strongest. if you go witch, then you need to fill out the colors and decide how you want to arrange your strongest color, since every crit will bring in 4ap of that color. if witch tanks, you'd end up with bringing in extra purple on top of what she produces, which she could use. or if you put someone like 4thor or Cyclops or torch (3* has to be in front of witch for this), crits would make red every time. this is why gsbw works so well because you can start stringing together her purple powers one behind the other and it is self sustaining.

dang, forgot kk. if tanking kk would make yellow strongest color, but could be put behind witch and that would work nearly as well as gsbw - that trio would be really good. if tanking thor would make red strongest color - not terribly useful, but probably a decent third if you wanted a separate damage dealer.