It must be quick adjusting for leg lengths. Anything that takes more than a couple of seconds (literally) to adjust is a no-go.

I prefer the lever-style quick releases for adjustment, but others swear by the better versions of the twist style. Try them both and think about it.

Stiffness and weight are the other two big considerations. The ideal tripod weighs nothing and is as stiff as a concrete foundation.

Finally, think HARD about a quick-release mount. If you have to twiddle the little 1/4" screw gizmo to get the camera on/off the tripod every time, then you won't use it. So decide on a quick release system, and then find a tripod that has it built-in (for weight savings).

Oh, and for still-photography, get a ball-head mount.

Cheers