I have two options:
A Glock 19 (9mm) that works well in a IWB holster.
A Kahr CM9 (much like the PM9, also 9mm) that works well in a pocket holster.
I went with the 9mm as something of a compromise. The .380 didn't have a good a track record from what I researched, and the .45 limits how many rounds you can carry. The 9mm is used by a couple of police departments with good success: with the right round it definitely has the stopping power. The Glock holds 15+1 and the Kahr holds 6+1 (single stack magazine).
It is largely going to be an individual choice, however. I would also suggest factoring in your physical size and style of clothing. If you're thin and wear only a tight t-shirt, a IWB holster with a 1911 probably isn't going to feel too good. Regardless, I'd suggest at least considering a pocket gun. They can do the job and are really easy to just throw into a pocket on your way out the door. There is almost no excuse for not carrying when you have one of those and you can carry with almost any kind of clothing.