Get the S&W 642 Airweight.
It is very very easy to carry and hide out. Drawing from a pocket is fast, and if you are ever uncertain of a situation, just put your hand in your pocket and you're ready should a need to draw arise.
It will also handle most defense situations we civilians might encounter. If I ever carry it solo, which is rare, I usually carry a reload. If it's my BUG, then no. Even with a relaod, it's not hard to conceal.
Just buy one, you'll never regret it.
PS: some people complain about the recoil and trigger. I have never had a felt recoil problem even with heavier +P loads. Just grip harder. Also, practice with it a lot one handed, as this is probably how it will be fired in a quick self defense situation.