If you leave out champs who haven't defended the belt that leaves:
Jones, GSP, Aldo, Cain, Barao, Mighty Mouse, and Ronda. I'm leaving Cruz out.
I'd say that Jones, Barao, Mighty Mouse, and Ronda are all dominant, leaving GSP Aldo and Cain.
I'd say GSP which is kind of a funny answer because he really is so dominant. But in his last few fights, there have been a few "oh shit he's really in trouble" moments that don't scream dominance. In contrast I never felt with any of the other champs on the list that they were in any real danger other than the Jones-Belfort armbar and when Barao got really stunned by McDonald.