Is the problem that the camera slips down? Or, is it that it's tippy if the camera is on it's side? (or something else)
If the camera slips and snugging the mounting screw doesn't help, you may need to replace whatever surface the head has to something that has more grip, or shim it with some hobby foam or some such to get better grip.
The larger ball heads are usually more stable than pan-tilt heads for setting the camera up for verticals. For pan-tilt heads, the Gitzo ones are nicely beefy and nicely made, though a lot more dear to buy than Manfrotto.