Colvin will have a good career, but if you look at all of the hype that Castro came with and all of the insiders saying he will be an All-Star shortstop for the Cubs for years to come, it should be a no brainer. We have seen good things from both, but Castro looks a lot more smooth in the field and a lot more comfortable in the batters box already, and he can't even legally drink yet.
If Colvin gets some time, he has the potential to be a big stick in the lineup, but IMO he doesn't solidify anything as much as Castro does.