I have both the style L33 has (mine's the Griot's one with the drawer under the seat) and the one with the round seat and the hydraulic (or is it pneumatic?) cylinder that allows height adjustment. I find I use them both and that any benefits of one seem balanced by benefits of the other. Can't say which one you'll prefer as I don't really know which one *I* prefer

But the height adjustable one, well, is adjustable, and when you want to be at a certain height that makes all the difference; so if I could only have one it would be the adjustable one.
I myself do *not* like the ones that have back rests on them. I find them less comfortable for actually *working* when sitting on them and I seem to tip over in them more often (when the wheels hit something). But that'll probably be yet another of those personal preference things where nobody can predict which you'll like. Just remember that doing work while sitting on one is different from merely sitting.