There are many different feet, but I think they fall into 2 different categories: darning-type and hopping. The darning feet are just that: made from plastic or metal, open or closed toe, they ride just above the fabric and are stationary as you stitch. Most folks like the ones that give good visibility, either open toed or clear plastic. The hopping feet have a spring in them and are usually installed in a similar manner to a walking foot in that there is a bar that goes over a part of the shaft that holds the needle (often the screw). And true to it's name, it hops. The foot goes down and applies pressure on the fabric as the stitch is taken, then hops up removing pressure on the fabric so you can move it. Sometimes there's a special setting that you need to make on your machine.
Unfortunately, it's a personal preference, and it's hard to tell which type you like better unless you try them. I would go to a Janome dealer and see if they will let you try the different feet to see if you can get a feel for them.