The main attraction of a ball head, as I see it, is high strength for the weight of the head. A pan-tilt head offers more control, because you can adjust each axis separately.
The best of both worlds is the Arca-Swiss B2, which uses two balls, one for each axis, so it's a pan-tilt head with the strength of a ball head, but it's a large head (3.5 lbs) designed to hold big cameras and long lenses (capacity 150 lbs!). The Z2, which is scheduled to replace it someday, will be smaller and more compact.
With a single ball head, like most ball heads other than the B2, I find it easiest to level using a round bullet level, rather than a single or double vial level, because the bullet level imitates the motion of the ball.