I have the Vibrant, and do like it, and there were alot of complaints about slow updates but it looks like Samsung may have learned from that backlash.
And people said that said Samsung might have learned from "the worst Android phone ever made", the Samsung Moment or the Behold II and all of Samsung's other devices.
The Sensation or the G2x will be your best choices. The Sensation with Sense is alright if you just want to use your phone without having to tweak it or anything. So is the G2x. The G2x is a bit buggy right now, but it'll probably be resolved very shortly here with the Gingerbread update.
Don't touch anything Samsung makes with a 10-foot pole. People say Samsung should be given yet another chance with the Galaxy S2, but that's what they said about the Galaxy S and look at the litany of problems with that phone (broken GPS, noticeable lag, wonky audio chip and piss-poor support.)
Go into the store when the Sensation comes out and compare it to the G2x. Sense might or not be your cup of tea, same with stock Android. Also, the 4.3'' display might not be for you on the Sensation.