I'd go with Ksport. They're COMPLETELY different than the junk they put out before. I've talked with quite a few guys at the track the past few times I was out there and all of them were talking about how much more solid they feel than before. Obvious differences were that the shocks are all black now, thicker body and black mounts, as far as function you'd have to call Ksport to find out cause that I don't know. Ksport is local here so A LOT of locals use them, probably half the imports out there we using them and I didn't hear any complaints. I'm going to order a set for my car here in the next few days.
I've owned Tein flex before (probably 2 years ago) and after a little while probably a few months started to feel sloppy. Never personally owned Megans so i dont' have any input on them.
Best bang for your buck in that line up is the Ksport. I just installed a set that Dusty hooked me up with. Really nice product, havent had a chance to really see how they perform yet but first impression is a positive one.