I would highly suggest that you shoot as many guns as you can get your hands on before you decide. I'm glad you have someone that is willin to teach you but you need to spend some time behind a pistol before you make your decision. Both the guns you mentioned are solid weapons but that doesn't mean that either one is right for you. Also, don't rule out a revolver or another caliber. You have to shoot what you are comfortable with and what you will practice with. Take your time in picking your weapon, your life may very well depend on it.
If the pain is lacking so is the discipline...
"the only 911 call I need is chambering a round" - Mr. Muller, MO car dealer