I'm flying a Science Vessel as of tonight. I flew both a Cruiser and Science Vessel in Beta and decided on the Science Vessel for live. It's got a lot of shields but the hull is weaker. There's some nice tricks with the Science Vessel that I enjoy as well. The maneuverability is pretty decent, but not as fast as an Escort.
All in all I love my Science Vessel. Oh, and in case you're curious, I'm an Engineer.
In the Beta I went for the Escort initially, but then scraped enough credits together to eventually have all 3 classes.
Escort was great, but in a mission where u are outnumbered I got a hammering - being an Engineering Captain helped to a degree, but not enough.
Next I tried the Science vessel as people were saying the shields were awesome and they were right - they got a nerf near the end of the beta but still good and still quite maneouverable.
Lastly I bought the Cruiser - same weapons bays as the science vessel, 2 fore and 2 aft, but man it flys like a pig stuck in tar. I ended up having to load a forward and rear torpedo launcher to get a chance to take out the big ships.
During the Borg encounter on the last day I was in my cruiser and switched to escort - the change in the way it handled was amazing, the escort could spin on a dime but trouble was I got 1 shotted most of the time
So anyway, now I plan to plump for Science vessel again in a couple of levels time. It seems to me a nice mix: fairly maneouverable, with great survivability and when u switch to boost power levels the weapons it still hits hard.
I played up to a T3 Science in beta but I've canceled my game order now. I was planning on going Escort though. Mostly because the game in it's current form is more zerg pew pew DPS chart than it is tank/"heal." I use the term "heal" loosely because it really doesn't exist outside of a shield transfer that will pause a death for 6 seconds or a hull repair that's only real use is to repair a tank faster once the combat is over. As a general rule once your shields are gone you're dead. So I don't see a real need for hull repair outside of maybe PvP. That's the only time I've seen hull repair actually become useful and only then because of the threat of stealth attacks. NPCs don't offer that kind of problem.