Cam Maybin definitely has the higher ceiling. I think he'll be a fine outfielder when he's ready. He has a few issues to work on before he's ready to be in a discussion for a legitimate callup like plate discipline and his avg/slug are inflated to some extent because of the poor defense (and field conditions) in the MWL. I think he'll have things straightened around by July of next year and will be in line for a midseason promotion to AA and from that point he'll be on the fasttrack to Detroit.
I realize that's pretty negative, so I'll touch on his positives. He is very quick. He can fly around the bases. He has shown tremendous power potential. He doesn't hit a lot of balls in the air, which is good because of his speed, but when he does he's hitting gaps frequently.
Evan Longoria is a nice prospect. Very good in fact, but just doesn't have the ceiling Maybin does. Though I think he is the safer pick.
I voted Cam Maybin.