I have both, both are fantastic ships and I would recommend them, in my experience the Fleet Nebula is bulky and tanky. Its also versatile with the universal LT. It flies more like a cruiser than a sci ship.
The Vesta feels weaker with a lower hull and shields but the maneuverability makes it deadly. Its also even more versatile than the Flt Neb which is very handy.
It really comes down to how you want to play the ship, the Nebula is more of a support ship (with Sci, then Eng as primary and secondary roles) that can have any tertiary focus you want. While the Vesta is whatever you want it to be for a secondary and tertiary role.
My Romulan Liberated Borg character made it to Level 30 and beat the (old) Defense of New Romulus with the skill point bug.
The Vesta is probably better in every way except for taking damage. Better firepower, more maneuverable, better toys, and if you went with the (expensive) 3-pack, you get 3 survivability powers: one for knocking away incoming torps and getting out of tractor beams, one for a very significant heal over time that affects both hull and shields, and an invulnerability bubble that has saved me from some of those crazy Borg plasma rings that are usually instakill.
Ultimately, the ship on its own is a bit of a toss-up. It's only if you get the 3-pack and are willing to sacrifice the console slots that the Vesta really becomes the gem of science ships.
At First excuse my Bad english but German is my Mother Language^^
I also Like the Nebula and i think i will buy the Fleet Version.
I have a SCI-Officer but i don't like him bad Captain Abillitys and it is not funny to Play him as a Healer in Space with a SCI-Ship,so i think i will delete him.
But i want the Nebula for a New Officer but no Idea what Kind of Officer?
A Tac or a Eng?
Maybe you have some suggestions for me (-:
Don't delete your sci... they can still punch out DPS with the correct BOFF layout but have superior defensive captain abilities, not to mention Photonic Fleet and Subnucleonic Beam to get rid of annoying enemy buffs.
Maybe i will Use The SCI Officer for a Hybrid (also a Escort or a Cruiser)
Have try to Play my SCI as Healer (Ground and Space) on Ground is ok but in Space it was not Fun to Play with him an most of the SCI SHips are not what i searching for (Optical) maybe he will Fly a Cruiser in the future