Best team fight specializations?

I just tried firebrand support and it was so damn fun pure healer and buffer my team would not die... What else is really strong in teams ? It can be damage/cc/healer

Scourge, reaper (when supported). Holosmith and to a lesser extent, rev and core guard.

Holosmith and Core guardian are right there on top IMO due to being able to stand on their own when required and also having moderate (for guard) and heavy (for holo) amounts of CC.

Scourge and Reaper are the absolute kings of teamfight because of their immense AoE potential and weakness/torment combo spams. They need a support to fully shine however or you'll be spending most of the time running from people trying to pick you up OR zerging up your kitten. For this reason most solo players use the blood traitline along with soul reaping and scourge (and some extra healing power like sage amulet). If you're bold enough and experienced enough with dodging the most damaging telegraphs of other classes, you could go full condi curses/reaping/scourge (or power reaper correspondingly) and still shine.

Revenant is a bit harder but has very high single target damage potential. You'll either get to kill all of them one by one or die miserably due to missing one heal or one dodge at the proper time. Anything else is better only +1 in teams and looking to pick off people and decap points like mesmer and thief, and even Ranger to some extent.