I've only disliked one or two jobs that I've played. Ninja and Samurai. But, when it comes to the jobs I like, there's just so many, for so many reasons!
I love Warrior because I like protecting the party by keeping the mob focused on me, and smacking it senseless with a Great Axe.
I love Black Mage because all I have to do is stand in one place and just RAIN Destruction down onto the mob. Even as an Elvaan, who are one of the hardest classes to play BLM effectivly, I love doing 300+ damage on a Magic Burst.
I love White Mage because it's a sure way I know I'm not going to die in a party for no reason. I've run into some crappy white mages, but I know when I'm playing WHM, I'm going to keep the entire party safe.
I love monk because of Hundred Fists <3, there's nothing better than going berserk on something when you're in trouble...