I dunno about glock... But 9mm over .40 any day of the week.
I have a Sig P226 & a Sig 229 (for carry) both in 9mm. I have friends who I shoot against in the uspsa and idpa that wont touch a 9mm 'cause its a "minor caliber"... But we all agree that it makes little difference what caliber you are being shot at with, if you are being shot at by someone who is "practically competant" with whatever handgun they are using; You are going to get bad hurt or dead... and fast.
9mm is cheap cheap cheap
you can afford to shoot shoot shoot
One side note: 9mm is the handgun caliber most capable of penetrating kevlar and/or other protective clothing/devices due to its small mass/high velocity. Most handgunners train to shoot center mass and will therefore shoot center mass when under duress. The .40 is practically ballistically designed to NOT penetrate kevlar (one reason the LE communtiy loves it; They dont have to worry as much about fratricide) .40 came about as a "happy medium" between .45 and 10mm after the somewhat overpowered 10mm problems in the LE community... 10mm is nice too...
Point is that kevlar is cheap and freely availible to anyone. If you are facing down a determined hardend criminal, they may well have kevlar on...

Just my 2 Cents...

I wish I could spell...