personally i ride the flow FSi pro model bindings - i selected them based on peer reviews for the right combo of stiffness, flex, and range of motion for snowkiting. they suit me just fine on the slopes, too. i'm a heavier rider at about 230lbs these days & they're not too soft for me, nor are they highly rigid. here's a google link i found to the ones i sport on my deck: Flow Pro FSi 2006 - Mens Snowboard Bindings @ ABC-of-Snowboarding
my bro rides with one of their carbon fiber models from a couple years ago & he doesn't seem to mind that they're super stiff... but from online reviews, i'd steer clear of full carbon fiber - from a couple horror stories i read, they're so stiff that some people have broken their ankles on landings! nooot my cup of tea.
really, it just depends on how high of a back & how stiff you want to go - which is determined by the type of riding you do. if you're a powder guy, go for a higher back. if you're a park jibber, go low so you can moooove. if you're on a tight budget, go with a plastic model - even they hold up pretty damn good. if you buy used, just don't bother with the oooold school aluminum backed ones - the backs tend to bend/warp out of shape under load from a bigger guy, which is so not cool in my books.