Just got my .40 today and almost wishing I'd got the 9mm. Ammo is cheaper in the 9 and it is a formidable round with the right ammo. Two reasons I got the .40 was in reading and talking with those that have shot quite a bit with the M&P .40. They said that it was that it's the lowest recoil .40 that they've ever shot. I typically don't like the snap roll of the .40. I usually shoot a 9 or .45. Another reason I went with the .40 is that a firearms guru friend said that usually the best calibers are the ones that are originally or first made for a particular model of firearm. I haven't even shot the thing yet and thinking of trading it in for the 9. Thoughts?