^This!!!
Plus - how can people who haven't used both know which they prefer?
Without experiencing both, you can only know if you like the one you've tried.
The OP already knows how Sense is.
Being someone who owns Sense UI, Vanilla Android, and TouchWiz UI android handsets, I believe I can be of some assitance here.
Vanilla - Ah my first Android handset. I actually prefer vanilla to any of the UI 'enhancements'. Why? Both Sense UI and TouchWiz handsets have custom framework that messes with some of Android's really cool functionality. Like pairing & using a Wiimote controller with my EVO, for instance.
Sense. Sense UI is ok. It has a few things that I do like about it, very few, in fact. The phonebook is terrible. The only thing I like about the phonebook verus vanilla is you can search by phone number through the dialer. I can't stand the sense launcher, what a waste of space. I immediately replaced the EVO homescreen with LP+ the second I got my EVO. (After yelling at the RadioShack guy from trying to install ATK on my EVO. He asked why, and I thne proceeded to school him in front of the entire store, which was during black friday weekend no less, so the store was packed. Guy shouldn't have questioned my wishes.) Actually to be completely honest, there isn't anything I like about Sense UI.
Sense UI is highly over rated, and messes with quite a few of the phone's functions. No thanks. Sure the eye candy does look nice, but that's not worth the performance drain/memory hog that Sense UI is. Especially since most if not all of the graphical elements of Sense UI can be replaced with a few apps, such as LP+.
Now on to touchwiz. The newer TouchWiz isn't that bad, actually. I find it much easier to use, and more organized than Sense UI. I especially like the widgets in the notification bar (which I added to my EVO, btw) for quick toggles while inside of an app/browser.
The main thing I don't like about these UI layovers is their heavy integration with social media. Facebook, twitter, etc. I really don't use twitter, so why is it integrated so deeply into my phone it's nearly impossible to remove without an AOSP build? (Thank you cyanogen!)
Your best bet is to see what phones are the most supported by home brew devs, as they will be your lifeline to keep your phone running lean, fast, mean, and updated long past when the carriers forget about your phone. (I'm lookin at you Samsung.)