Long time tank player here. Currently my favorites are DRK and GNB, followed closely by PLD which I have a love/hate with. WAR is my old love, but they chopped off its balls and made it feel way more stale in this era, somehow by taking away real Berserk. For fun I'd recommend GNB or PLD.

I do have a caveat about DRK though. They fucked it up. In trying to homogenize the tanks, they butchered it fully this expansion. This is suppose to be its expansion, and it just doesn't feel as groovy as it should. They should have changed the animation for Delirium, because it used to just give you MP and elongate the duration of Blood Weapon and Blood Price. Now that it's for a burst phase it doesn't feel appropriate, and the animation hang on Bloodspiller starting has cost me my 5th more often than I care to think about. Not only that, but it has no actual burst phase outside of getting to do its strong move 5 times, whereas WAR's at least still buffs the hits to their automatic highest damage potential. If it weren't for the Esteem shade you can conjure, it wouldn't feel strong at all. Also I miss the MP and Blood juggling game from last expansion. I didn't think they would make it any simpler, yet here we are. I'm actually one of the few that miss Heavensward style Darkside drains MP dudes. I mostly console myself in that Flood/Wave of Darkness or whatever is a take on Cecil's Dark Wave from FF4. Oh and Stalwart Soul is cool looking, but I feel the name is mismanaged for being an attack name.

That all said, DRK is my preferred tank for dungeons still. While it no longer has the advantage of being the only tank able to sprint without compromising its ability to tank and deal AOE damage, because of Flood of Dark/Shadow, it doesn't have to wait for a second GCD pretty much ever to solidify pick up on enemy groups. GNB is annoying in this regard, PLD a little less so, since at least Circle of Scorn timer is low. WAR can uhm, burst with Equlibrium heal to generate hate while moving, but the CD is long.