My favorite is the TOS Enterprise, closely followed by the TMP refit. Everything else is far behind.
As far as aesthetics go, I've always been reminded of a person without arms, when looking at the TOS ship. The saucer is the head, the secondary hull is the torso, and the nacelles are the legs. There's a rough parallel with function, too. The saucer "thinks," the engineering hull "metabolizes," and the nacelles "walk." I guess it doesn't need arms because of the tractor beams; and just from the proportions and the layout, the arms don't really seem to be missing, either.
Funny, then, that I also see the Starfleet arrowhead badge as a five-pointed star with two arms ripped off.