Lots of variety in the answers which shows that there is a ship for everyone. I'm assuming its fed ships that are being asked of so for me it would have to be the Excelsior class. To me it is a very nice evolutionary step from the constitution refit, which is my second favourite.
The refit just looks right
, adapted for the then modern style without taking too much away from the original ship. To me it doesn't seem to have dated too much, I think the design could sell well today if shown for the first time. The long scene which shows off the refit in TMP is still one of my favourite scenes from the entire franchise, the way the music matches the imagry still works so well.