Depending on era:
TOS - The Davids - love this design..
![](http://www.themackiestuff.com/ships/images/davidstos.jpg)
TMP - The Belmont - I love Ambassador variants on principle, but this is just sharp
![](http://www.themackiestuff.com/ships/images/thumbs/belmont.jpg)
TNG - The Armada - nothing says,"I'm going to kick you in the nuts till you puke" like the Armada does.
![](http://www.themackiestuff.com/ships/images/thumbs/armada.jpg)
Favorite overall? I'm going to go with the TOS Davids, just because it'll probably otherwise be overlooked by the masses, and I think this really should get some mention.
![](http://208.57.228.4/ubbthreads/images/graemlins/wink.gif)
honorable mention(!): The Rosa Class. Having the WWII inspired design fighting element (and Scrooge McDuck) is just awesome and completely original in Trek ships (afaik).