Hmm...depends on what ya want out of it.
Fire savant is good for crowd control, but loses a fair bit of effectiveness in later levels because many opponents either have resistance or immunity to fire.
Earth savant is good for damage over time, and acid retains a fairly level rate of effectiveness throughout the game...least, that I've seen, of course.
Water savant starts out kinda weak, facing a lot of undead in the early game, its effectiveness is pretty low, but it gets much better after about level 8-9 or so, when you start facing things that -aren't- undead. Also, apparently quite good against daemons.
Air savants are great for early game daze-locking foes, due to Sound Burst and Electric Loop, and they're also good for single-target spiking. Once you get Ball Lightning and Chain Lightning, however, you also get a really good boost in crowd control effectiveness. Also, with Air Savant II (at level 12), you get a permanent feather fall toggle, which saves you a boot/cloak/ring slot that you've got taken up with a feather fall item, so you can use it for something else. If its boots, I'd -definitely- suggest striding. Great in case you've gotta get the hell outta dodge.