i had union forces last year and didnt like them. i dont really know which i prefure. i heard flexier have more forgivness but i feel ill have more control with the sharks.
I would HIGHLY recommend, if you can, trying out some bindings with canting. I had a boner for canting initially, and when I tried it, it felt Reeeeeally fucking weird. I have malavitas,with auto cant, and while I love them, I have to bang my stance out hella wide to feel comfy on them.
Oh, for what it's worth. I rode some 2010 malavitas which are kiiiiinda like the cobra shark but not on a disc and liked them. Good value on the sharks too.
I havent' ridden the K2s, but someone can comment on that.
More questions, what kind of park riding do you do?