I think it depends on what you're doing.

Paladin looks like it wound up with a case of "if it ain't broke, don't fix it". It still stands as the king of defense, got more QoL goodies, and still seems like the prime choice for anyone who is either still new to tanking or just doesn't like change that comes with an expansion. Yes, block nerf sucks, but block's still there and is still pretty powerful.

Warrior I feel took the brunt of damage to identity with the change from being health and healing-based to winding up more in-line with other tanks in terms of passive mitigation, which does make it feel a teeny bit on the boring side. The upside is that it still does retain its more aggressive rampage-y gameplay and has also joined Paladin for being a good job for learning how to tank. At the end of the day, if you liked Warrior before, you'll still like it, and if you didn't like Warrior, then no one cares.

Dark Knight definitely wins the "most improved" award, and I'd argue that those whining about the job now are just players who got too used to how it was in Stormblood and need to move on with their lives. While it does lack a bit in the self-sustaining department compared to Paladin and Warrior, it definitely makes up for it with The Blackest Night being a lot more powerful and the satisfaction of popping Abyssal Drain on more than six targets. The only bit of advice I'd give though is not to get too cocky with TBN since that can promote bad gameplay, which usually leads to nerfs.

Gunbreaker....I'm thoroughly convinced that this isn't a tank. It feels like some dev designed it a DPS job saying "I'm a tank too" as a joke, and nobody got it. Its unique defensive cooldowns feel too much like an assortment of tinfoil hats, Aurora seems like a band-aid to fix a detached limb, and its the single closest job I've ever seen embodying the term "button bloat". While it can be fun to play at max level, that's still 20 levels of agonizing gameplay equivalent to driving a stick-shift with a shoddy transmission as you repeatedly faceplant that GCD timer. Sure, there will likely be some tweaks and adjustments along the way due to it being a new job. For now though, I'd only recommend it to people that want to play a tank, but don't actually want to tank.