Get a .40. I would steer clear of the 9mm. You want something that will get the job done. I know that will start a ruckus but you never hear a debate about a .45 and .40 being enough but the 9mm is always in the center of the the debate about what is enough gun. I think there is a good reason for that.
I will say it then. The 40 and 45 are both underpowered and, especially in the case of the 45, highly overrated.
"Those who would give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety."
- Benjamin Franklin