Stock Android really is the best experience. You can tell it was designed with a sort of consistency and fluidity that all of the manufacturer skins lack. I would also take a Galaxy Nexus over any skinned Android device; with the exception of HTC Sense, which has really improved since the disastrous Gingerbread days.
I just install Aviate or some other thing on top of TouchWiz on my Galaxy 5. Who cares what the default UI is like, you can replace it is enough on Android. I think you can get any kind of Android UI you like, you're not stuck with what you get from the manufacturer.
Not all of it. In one of the recent HTC updates they pushed some incredinly inane "features", for instance a "volume warning" that forces you to click ok to move the volume past about the halfway point - even if it's the BLUETOOTH volume.
I'm pretty fond of Sony's (generally mild) changes from stock from the 4.0 era on. These days they seem to put most of their efforts into apps (where it belongs) to differentiate the camera, media players and so on.
