Hehe, I am in the same situation. If I decide .40 i can go down to sportsman's warehouse right now. but i think 9mm is winning so I am waiting to find one.
I believe it comes down to finance. What can you afford to shoot?
if its just for the range, there is really no reason to pay more for a similar sized whole in the paper.
defense....1mm size in difference...um...
On this board I have read a lot of people with 9mm saying its the placement of the shot. Yes well, if I shot someone with a .40 in the same place as a 9mm, I would prefer the .40 for logical reasons. its 1mm bigger. but since i am going to be enjoying my gun for recreational reason more, in hopes of becoming a better shot...9mm seems more economical to me. If I wasn't a poor college student I would take a .40