I have to go with the TMP Constitution class. It was just a work of art. Truly, the feather in the crown of Starfleet ships.
Another personal favorite was the Intrepid class. I thought it was beautiful, functional, and just a dream to watch.
It's not mentioned in the thread, but my least favorite was the Defiant class. As far as I'm concerned, it's an ugly war tortoise.
Agreed, I love the Intrepid Class, the coolest class of Star-Ship in the Fleet. Reguarding the Defient, IMO it's the A-10 Warthog of the fleet, not to good looking, but very rugged, powerful engines and TONS of firepower at it's disposal...