Recoil wise I couldn't tell much of a difference. They're both small guns, so its a little zippier than in a full size pistol, but no big deal. I went with the G26 because I already had nines and the mags are interchangeable. Add this to the fact that 9mm is cheaper than .40 and it was a no brainer. If I were starting from scratch, I probably would have bought the G30 in .45. .40 always struck me as a somewhat silly compromise caliber. Not tht much better than 9mm, and not near the oomph of a .45. Nothing wrong with it, it just doesn't seem worth the extra ammo cost. Your mileage may vary.
FQ13
Actually, I agree with FQ's statement. One is as good the other..... if you have it with you when it's needed. I also (at one time) wished I'd bought the G30 instead of the G27, but I ended up re-thinking that one during the great ammo shortage of 2009........ because around here, the ONLY handgun ammo available on a regular basis was .40 S&W. So I was able to shoot and practice more with the G27 than if I'd have bought the .45 (still can't buy .45 ammo around here).
Anyway, the G27 is a great gun (and I was once a notorious Glock hater). I like it for it's size/weight/power. And, for a short barrel, it is scary accurate. I probably won't own another Glock (unless a too-good deal comes along on the G30), but I won't get rid of my G27 either.