Blue Mage, foremost and forever.
Not only is it a hybrid-style battlemage type of job most consistently throughout its implementations (enough to cause it to be a core part of the job identity - with a couple outliers, but a lot of jobs see outliers periodically), the unique and generally-eccentric style of acquiring new spells as well as thinking about how you're supposed to use them makes for an eclectic and unorthodox mentality on how to go about combat. It just makes everything else about their games so much more interesting. The implementations in FFTA, FFTA2 and FFXI are among the better ones, with the latter being what the series should really use as a model for it going forward. Bravely Default deserves an honorable mention for the Vampire job being pretty great on its own.
It's supremely disappointing that they took the direction they chose with Blue Mage in FFXIV.
Second favorite job would probably be Mystic Knight. You might start to notice a pattern here of mixing swords and magic together. Bonus points if I can mix these two jobs together (like in FFV or Bravely Default).