Either Colt government 1911, Colt Commander, Kimber BP TEN II when I feel it might be a 14+1 day, Glock 30, HK USP Tactical in you guessed it .45, Colt Defender, Glock 36, even on occasion Colt Gold Cup but that rear adj. sight will cut you up something awful.
Always .45. Typically I carry an old Goverment 1911 I figure after I run out anyone still moving I can club to death with it.
I now see after typing this I may have a bit of an addiction to the .45 and if you knew how many colts alone I had you might agree, I bet drugs are cheaper but guns are a blast.!
I started carrying the new Taurus TCP 738 when I bought it a year ago, in the summer months, due to its light weight, small size and easy concealability, but in the very few months of winter, it gets religated to backup and I carry a .40 S&W inside the waist band under my jacket. I like the fact the .40 carries 14 in the mag and one in the pipe and is DAO with a fairly stiff trigger/safety. All of my nines are just as big as my .40's and the extra couple rounds of nines don't make up for the inital extra stopping power of a .40 +P JHP.
If we were allowed OC, then I would most likely opt for something even larger and more intimidating that I could shoot with quickly, comfortably and accurately. Like one gent mentioned, regardless of caliber, if you don't hit the target . . . .the threat may win the dispute.
I find my great grandma's Colt Vest Pocket .25acp in my pocket more than anything else currently. I also carry .38spl and .45 acp. I really am looking at the Kel-tec 9mm though now. I'd love to get a Colt New Agent at some point.