I'm right there with you. There are basic similarities within most job roles (for example, each tank will have a throw, an AoE combo, a single-target combo, a smaller mitigation, a larger mitigation), but there are also very unique things to each class in my opinion. I'm in the same boat where for tanks, I love playing PLD and to a somewhat lesser extent WAR, but I can't really get into DRK or GNB. For healers, it's SCH all the way, with WHM on the side (AST has been growing on me recently as I level it, but SGE I can't get into). For DPS - it's RDM, BRD, and DRG to take one of each role. Haven't really been able to get into any other DPS classes.

And why? Because I find them all very different in unique ways once you get past the surface similarities of having a shared basic kit of moves. Each class has things that make it completely distinct from the other classes in its role. My own mind can't wrap itself around this "all jobs are the same" idea, either.