My .02 is you should go with a 40 cal... It has a little more A** behind it when it comes to self defense and you only lose a couple of rounds when it comes to magazine capacity. If you can get someone who reloads the ammo cost wont be so bad.
As for brand I recommend Glock or Smith and Wesson along with any other reputable brand... As other people have posted go to the gun dealer and pick the gun up to see how it feels in your hand. I would also recommend night sights on your weapon... statistics have shown that a majority confrontations happen in low light conditions so be prepared!
I would also recommend taking some basic, intermediate, and advanced handgun classes if possible.