I currently have 2 fascinates and a Tbolt on my account. I actually have a pre plus also, but won't talk about that right now.
Personally i went from the incredible to the fascinate to the Tbolt. There are things to like a lot about all 3.
The incredible was pretty awesome when i first got it, but the desire for larger screen and some hardware problems i had with mine (camera locked up phone regularly) ended up in an exchange for a fascinate.
When i first played around with the fascinate i missed a lot about sense. Sense in 2.2 had much better exchange integration for instance. Meeting requests that i would receive on my phone actually showed the time of the meeting and if there was a telephone number in a calender appointment on my phone i could just click the number and the Incredible would dial. As i do a ton of conference calls, and sometimes work at home from my cell, the lack of features that well, make sense, in touchwiz really bothered me.
The upside was that the fascinate ended up being quite a good phone. The battery life was much better than the incredible and once you got rid of some of the bloat and removed the crappy samsung widgets it was quite fast. Add to that the truly incredible screen (which frankly is as good outside as my Tbolt) and it is a nice phone.
Granted it doesn't have 2.2, but i did, so while i sympathize with people who are crying for 2.2 on the fascinate, it really wasn't a huge deal for me.
Additional benefits included the very nice audio subsystem, the GPU, and Odin.
I can't stress enough how awesome it is to always know that almost nothing you do to the phone can really brick it as ODIN can bring almost anything back from the dead. It also makes the phone stupidly easy to root. I probably miss this from the Samsung more than anything else.
Sense is more responsive to touch inputs than touchwiz, and this is a large part of why the Tbolt feels so fast. The screen is quite nice (even next to a SAMOLED), and I've gotten the battery life to where it's acceptable for me. I like the Tbolt more, but some of that is because it's new. In truth, you can't really go to wrongly with any of these phones.
To say one is awesome and the other sucks is distorting reality quite a bit as the differences between them are pretty fine.