Governors have more administrative experience than Senators. That's in the nature of the positions. So someone who's been Governor for two years has more experience than someone who's been a Senator for one.
Christie's also older, and in Ann's eyes, his earlier experience as US Attorney probably trumps Rubio's in the State Legislature. Either would probably complement Romney, appealing to groups Romney would have a harder time with.
Kyl, by contrast, comes across as pretty white bread, more like Romney than different. No ethnic appeal.
The only two people that would have me reconsider my decision not to vote for Romney are Perry and Jindal. Both are about as independent of the GOPe as possible for a governor. Christie would do a good job as an attack dog, but his positions are too moderate for my liking.