I like .40 caliber in gen 4. There's lots of of this ammo coming back on the market now & with a glock, you can shoot the cheap Russian stuff until the prices come down. Gen 4 gives you grip options and reversible magazine release. Being a lefty, I see this as an advantage over earlier Glock generations. Also, you can get extended mags for your range sessions. So there's my two cents.
Yea though I walk through the valley of the shadow of death, I will fear no evil. My rod is a GLOCK and it comforts me