I didn't read all the responses yet so pardon me if I repeat something that's already been said.
I go with Skate for a couple of reasons.
First of all, Sawyer is hot as fuck! Don't get me wrong, Jack is hot too but DAYUM! I don't usually go for the blond, blue-eyed type but Josh Holloway is my exception.
Second (and most importantly) of all, Sawyer is what he is, Kate knows him very well, much better than Jack would ever let her know. Jack is very troubled, bordering on nuts and always has been. He felt the need to be leader from early on and in such a way that it felt narcissistic. He thinks it's OK for him to keep things from other people around (who trust him) but he gets psycho pissed when he finds out that anybody has the nerve to keep something from him.
Sawyer almost smirks when he finds out something he didn't know. He also did something Jack would never do: He jumped out of the helicopter in an effort to save the rest of his friends, he did that (I feel), mostly for Kate. Jack was so obsessed with getting off the island that he was probably considering throwing Hurley out.
Sawyer can be underhanded but (unlike Jack) he doesn't pretend not to be.
Ultimately, Sawyer is a better match for her because he can understand her in a way Jack can't. Also, their chemistry is sooooooooooooooo hot! When Kate and Jack kissed that time, I personally thought it was weird....it felt more like a brother and sister kiss.