Personally I am a 40/45 fan, I just like a bigger bullet. Having said that I do sometimes carry My shield 9mm or Glock 26/19 and feel pretty comfortable.
Generally its my Glock 23 or My shield 45 both guns are utterly reliable and accurate, My shield is amazingly accurate for such a small gun, which gives me a little more confidence while carrying even tho the magazine capacity is limited.