BLM is unequivocally the best-designed class/job in any MMORPG I've ever played (and I've played a lot of them). It flows perfectly. It has procs to vary the execution - but isn't dependent on them. It has plenty of optimization nuances to master, and it rewards you amply for doing so. It's designed around a core weakness, with tools that help to mitigate that limitation without trivializing it. All of that adds up to a class that must adapt itself to each encounter, ensuring it stays engaging throughout content cycles.

(And perhaps best of all: it's not reliant on stupid crit RNG.)

DRG is also incredibly well-designed now. I could think of one or two little things that it could use, mostly to help maintain its combo chains during unavoidable disconnects and whatnot.

PLD is very well-designed now, too. There are gripes to be had that concern the direction they've taken the tanking jobs collectively. But for what it is, PLD plays smoothly and has little room for improvement.