I was carrying .40 when I tried a friend's 1911. That hooked me and while just "cruisin'" in my favorite gun shop (Four Seasons Firearms), I spotted one used for a great price.
I can shoot the 1911 more accurately and consistently than any other gun I own. It became my primary carry gun (if clothing/occasion allows for it).
If the planets align correctly, I should have an M&P .45 by late next week. Shot the one out at S&W's range and really liked it. We'll see if it becomes primary after working it out for a while.
I'm a believer that the biggest gun you can carry and shoot accurately is the best choice. So that's how I make the decision.