I almost worded this poll "what class do you play", but then I realized that many people play more than one character and more than one class, so this seems to be the only way to word this. Anyway, just for fun,
Engineer. Love the tank ability in space and that my main owns all the ships in game. Summoning things with Bunker Fab Mk X is quite nice as well.
I've been round robin-ing each my 5 Toons...
Started with a TAC in Escorts and Cruisers...
Then a SCI in SCI Vessels (naturally)...
Then ENG in Cruisers and Escorts...
Then a Klingon TAC... (got bored with Him and discovered rather quickly that I SUCK at PvP)
I'm back to a TAC using just Crusiers now.
I think that with my vote, I'd go with my Engineer so far... compared to my experiences with TAC and SCI at this point I've found that the ENG Class has the best offense/defense on the ground and even though I prefer Space Combat, there is a lot of Ground Combat in the game.
(I play on Advanced for both Space and Ground Combat)
The TAC ground abilities are OK and you can survive fairly well in almost all instances...
But the SCI ground abilities are very lacking, I died a whole lot more on the ground with my SCI toon and found it very difficult to almost impossible, to complete many of the ground missions on the Advanced level and had to go to the Normal mode quite often.
The SCI's Ground Abilities (IMHO) are way under powered and often I found the cool-downs to be way too long.
In space combat, all three classes are fun to use so I don't have a favorite there.
I was tempted to put science. I mean, science powers are pretty damned fun. This would be my pick if going only by gameplay.
However, in the end i'd have to say tactical. Effectiveness of tactical powers aside, there's something admirable about tactical officers, especially in STO when we're at war (both Fed and KDF). Especially so for KDF, you'd imagine that tactical are where all the best warriors are at.
Feds are no slouches either, we can even learn close-combat skills applicable to bat'leth combat. And i've never bought the fact that many starfleeters say they arent military. From military ranks, to terms like 'command', heavily armed ships and mandate to protect the federation...well yeah. Im not belittling exploration and diplomacy, but when we're at war, tactical is in the forefront.
BUT. I would emphasize that my reason for choosing tactical isnt that it kills stuff fastest. Sadly, i imagine the huge glut of tactical captains in the game is due to this reason.
I think one of my problems in choosing is cause all my science captains are in sci ships. I have an engineer in a escort and a tac in a cruiser. I see a lot of sci in BoPs and escorts and I wonder if I'm missing something.
I love my tacs the burn through everything so fast. And my engineers can live forever in a firefight.
My healing on the ground is getting better but playing the offensive as a sci is very fun.
Well I havent played science yet, but I have a Caitian VA engineer on the fed side (flew escorts from the start, though i've been trying cruisers/science ships now at VA) and a Klingon BG3 on the klingon side (flying carriers, though used battlecruisers up to this point).
The tactical does have quite a few survivability issues on the ground, IMO - but that's probably just me being spoiled by all the engineer survivability powers that I got used to while levelling up. On the flip side, my tactical is more more 'interactive' on the ground (a lot more abilities I use frequently) than the engi, and does quite a bit more damage. I have the tactical specced for a mix of dual pistol and bat'leth combat, specializing in the close combat kit and abilities.
On the other hand, my engineer (who runs with two engineer away team bo's) can set up 7 phaser turrets before pulling, and that pretty much melts anything that gets into weapons range. I've considered going with 4 engineer BO's so i can have 13 phaser turrets out at a time but I havent gone through with it yet, I like having my science bo's healing and tac bo's support abilities/debuffs.
In space, I've found the engineer's abilities to be a little inadequate... they're useful sure, but they dont seem to have as big an impact when used as the tactical's damage-boosting abilities. I only really notice the engineer's power when I get overwhelmed by enemeis and the combination of EPS power transfer, rotate shield frequency, engineering fleet, and miracle worker - combined with my engi and science bo healing abilities - keeps me alive through insurmountable odds.
I'll be trying a science officer in the romulan faction once they're released, but until then I'll have to say that my engineer is my favorite - but mostly because it was my first character and the one I'm most comfortable playing.