I took all the classes to 50 back in 2.x so I could determine which ones I felt the most comfortable playing. I settled on bard as my main DPS (still like it even after 3.0) with a side helping of SCH and WAR for healing and tanking. I like them because the rotations for each job can change up on the fly depending on the situation. Bard is the most flexible DPS, SCH is the most adaptible healer, and WAR is the most self sufficient tank.

I still jump to other classes all the time, though. I'll eventually get them all to 60.