Most people don't like them because they're not the fanciest, but my Ruger LCP is always in my back left pocket and no one is ever the wiser. Just my thoughts.
If I was going to carry a back up gun, it'd be on the same platform and capable of using the same magazines (or at the very least same caliber) as my primary. It'd also be a place that is easy to get to from my non-dominant shooting hand, in case it is disabled. Seems to make the most sense to me.
I like the Kahr CW45 since it is made in America. That means something to a guy like me. I picked one up recently and it is a really nice gun for the price ($350) and would make a great BU gun. I shoot and reload 45 and sometimes want a smaller package than my fullsize 1911 for extended carry. I dont have the cash to put down for a compact 1911 so this fit the bill. After shooting it I am pleasently surprised how nice it shot and may just keep it longer than expected.
I read a artical they tested a xd 9m and a glock and beat the hell out of both and the glock was kia but the xd survived to shoot another day, so does everybody have to have a glock? Whats so awsome about them?
Looks like you have several good suggestions for back up guns. So what I want to know is where this article might be found so I can read about this Glock that was "KIA". Unless they are literally beating the hell out of the guns, I'm gonna preemptively call BS.