I shoot .45 1911's in IDPA - CDP and USPSA - SS. Have for .... 5yrs.
The .45's are the most reliable of all the other calibers, in my experience. The design was/is meant for a .45 230gr RN bullet. Get fancy with the bullet shape (hollow points, SWC) and there can be issues, but gunsmiths have figured out how to make those shapes work well, too. And you don't have to reload all your ammo; store-bought works perfect.
The .40 bullet shape is hard to make reliable in the 1911 format. 9mm is, as well, but there are occasionally some very reliable 9mm 1911's around.
But for self defense, what's more intimidating -- in a pistol -- than staring down the barrel of a .45" hole?