STAGE 2 said:
You are going to get as many different replies as there are posters, some with lengthy statistics and some with cute little quips like "9mm may expand but .45 will never shrink"
Damnit man! You stole my line!
Seriously - I would also vote for the .45, although I admit I have never shot a 40 caliber. However, I did own a 9mm, and I have heard the kick compared to 9mm quite frequently, and more often than not the word of choice is "snappy." That's exactly how I would have described my Beretta 92. My cousin recently purchased a S&W Sigma in .40, and he described his first trip to the range as "unpleasant," and complained about a numb trigger finger due to heavy and (once again) 'snappy' recoil. I've also heard .40 referred to as "the worst of both worlds," describing the push of a .45, and snap of a 9mm.
I plan on renting a Glock in .40, or maybe taking my cousins S&W to the range one day to see for myself. The reason I would have to cast a vote for the .45 is because after owning several smaller calibers (.32, .380, 9mm, .357 mag) I simply find that it's what I shoot best with, and I can shoot very quickly and pretty accurately with the .45 - I also find the recoil more pleasant (big slow push upward vs. quick snap straight backwards) and trust the round a little more, but this is only my personal bias.
And STAGE 2 is right... .45 doesn't shrink
Sorry, couldn't resist.
Shoot both, and see what you like best... Both rounds will do the job just fine if you need them to, that's for sure. Have fun, and good luck with whatever you choose!