Eh, I quit a while ago, but here’s my 2 cents.
My favorites across the categories were the Gunbreaker, Sage, Summoner, Dancer and Reaper
The Gunbreaker is a tank class that almost plays like a DPS. You get the short queues and survivability of a tank, plenty of buttons to push and a killer aesthetic featuring the silliest melee weapon to ever be devised.
Sage was the only healer that clicked with me, aesthetically and mechanically. You have a hot on the tank, a lot of OCD skills to heal up raidwides and the occasional blooper, and some decently flashy damage skills. Along with some “stop dying already!”-buttons for the tank. Sadly, no matter what healer I tried, I tended to get piss-poor tanks who though mitigation was some kind of fried eastern street food.
Black Mages are involved and do massive damage. Red mages are flashy with a killer aesthetic. Summoners can be played half-asleep with nearly the same DPS as the red mage and a killer aesthetic to boot. Not my proudest pick, but a safe bet if DPS was needed and I was unfamilar with the content. (I usually ended up tanking, anways…)
Dancer was the least annoying picks in the ranged DPS department. Mechanist is something for people with better reflexes, more fingers and/or better latency than I had. Bard was dull as dishwater.
Dancer allowed me to wear the ranged DPS gear (like, say, Amon’s suit) while still having fun and engaging gameplay.
Melee DPS, my choice was reaper. Killer aesthetic, big hits, comparatively low APM, and you got that nifty teleport move that actually worked (as opposed to the dragoon’s jumps, which had too much cooldown and tended to move you to all the wrong places). Ninja is also fun, but was incredibly busy, not to mention their gear was unique to them, which meant no recycling.
Monk was okay, after the rework, but the visuals were pretty sub-par, coming from reaper and ninja first.
Since all story dungeons can now be done solo with the AI, you can pick whatever you like, but I did enjoy running those with the guild. Faster and usually some competent players around.