Lots of people use ball heads, but personally i like to be able to have seperate control of the different axis, or at least have seperate friction in them (see below), if you know what i mean, so that it's easy to pan sideways without moving the head on an up/down axis. Geared is good if you want to be able to make very precise adjustments for non-moving subjects.
I would say go into a shop with your camera, and ask if you can try putting it on the various types, and imagine taking the kind of photos you normally do, and see whether the tripod does what you want to do normally. My cheapy Velbon tripod head has a single release handle for the two panning movements, but the friction in the two movements is independant, so turning it sideways doesn't make it tend to droop, unless you loosen the handle too much. That's what i don't like about ball heads.
I would strongly recommend you get a quick release head, and get as many quick release plates for it as you have cameras. If you use your cameras hand held a lot, it's beneficial If the qr plate is unobtrusive so you can leave it on all the time and it won't get in the way.
I'd definately suggest you get a quick release head too, it makes it so easy to put attach/detach the camera from your tripod, and you can get most heads with this feature.
As for head, i'd recommend a geared head, as it allows you to make some very smooth movements - more for use in video rather than photos albeit
my fabulous SLIK, sadly relegated to the loft because I (shamefully) lost the quick release in a wood, had a three way handled head.
One for x around, another for y forward and backward, and a mythical z for angle (to turn it from horizontal up to vertical)
All with a handy twisty lock to make sure that once you move the camera with the handles it stays there.
In this case, the head was properly attached to the tripod (but then the tripod had another handle for height too), but the idea behind 3way handles is there.
If i'm not mistaken the head Cheeky has just described is also known as a Pan and Tilt head. Which is what i've got too, and i'll also gladly recommend.
My advice is to get some with little spirit guides too, so you can see if the camera is perfectly level or vertical. It probably won't cost any extra, but its really useful.
