Mountain Biking - Spring Terms

Hey I've been looking at different types of forks lately on websites and ive noticed they all have different types of "springs" ive come across air, coil, u-turn. what do these terms mean? and are there other terms out there and what do they mean? also what's the best?

Air is just that. Compressed air to control the sprung rate of the fork.
Spring - springs the can be preloaded by tightening the springs.
U-turn - Rock shoxx uses this and I believe it is a way to reduce travel.

I prefer spring forks as I find the travel is more plush and better suited to my style. It also TENDS to be stronger in rough situations. Every company has their own terms that apply to their forks. Going through them all could take some time. Ride both kind of forks and figure out which you prefer. Xc guys usually prefer air as it is lighter.

U-turn is a travel adjustment feature that allows you to change the amount of travelin your fork cranked down for climbing or cranked up for decending.