I chose the Nova class for my campaign. I liked the look, the size and the ability to enter atmosphere for planetary survey. I liked the fact that it was primarily a science vessel, and that the crew would have to be able to size up any opponents and resort to diplomacy/imaginitive solutions, as it is definitely not the best ship out there. It makes for better drama.
Also, I wanted a small crew to have to develop, and being so small, it gave me a realistic reason for my new academy grads to be included in senior staff meetings, etc. A smaller pond, so to speak to grow in.
Impressive despite its size. I am playing a post-dominion war era campaign with the exploration and contact of new alien worlds for evaluation for federation acceptance as a mission. Besides, there are real threats out there and I do not have to worry about canon vs. non-canon issues, and the players can make a huge impact without it influencing what has transpired already in DS9 or other shows.
I am having a blast with it and even if you don't feel the same about the Nova, maybe seeing my reasons for choosing it may help you in choosing a ship for you...
Best of luck to you! Take care.