Personally, the .40 is very popular with cops, but in reality, the 9mm is a perfectly adaquate man stopper.
The idea of 9mm being "under powered" stems from military experience I think, at least complaints from the military was the first place I heard of 9mm complaints. the problem is, the military can only use FMJ roundnose ammo. they can't use hollowpoints. dump a couple CorBon powerballs or Speer Gold dots into someone and I promise they ain't going nowhere fast. ammo type and shot placement.
Now if you wish to carry .40, you are certainly free to do so, if you want to carry 45 ACP, you're free to do so, if you want to use some oddball cartridge like .357 Sig, or 10mm Auto or .45 GAP I will not try to discourage you from carrying whatever you want.
I personally think there's nothing wrong with 9mm though, currently my only handgun is a .38 revolver, and I love .38 too. when it comes to .40 and .45 ammo is expensive, you carry fewer rounds per mag, and if you're a good shot it really doesn't help that much.