Which handgun is more powerful? 9mm handgun or a .45 cal handgun?

I know this may seem like a dumb question but I am an idiot when it comes to firearms. I purchased a Sigma Smith & Wesson 9 mm SW9VE handgun about 6 month ago and go the range often and I love it. (click here to see--> http://web.quick.cz/terc/saw/sigma.jpg ). I have been looking at some .45 cal handguns to upgrade to and am just wondering which is more powerful and will have more of a blow to intruders/invaders when using for self defense/home protection? When I go to the range my 9mm sounds like a BB gun/Pellet Gun compared to the .45 cal the others shoot. If a .45 cal is better then a 9 mm which ones would you all suggest being that I love Smith & Wesson? I am open to try another market or brand of .45 cal handguns but want a dependable one that is not a revolver. It must be an automatic handgun. Any good answers to my questions or suggestions would be great. Any links to some that I can look at would be great also.