Coming from experience....I would say the 9mm. I am a young woman that has to travel for work alone all the time.....gone for 3 or 4 days at a time several times a year to areas I've never been. When I started this job, my husband (already had a ccw) and wanted to introduce me to handguns and protecting myself. I took a wonderful class with an incredible instructor in West Virginia. This man took me from a very intimidated, terrified of handling a gun "child" to being very comfortable and very confident with myself with a glock 19 in 8 hours of instruction! It was incredible!
Anyway.....4 years later...I still own my glock 19, carry it everywhere (where it's legal to with my ccw)....and swear by it! I have made very few changes to my glock 19 and still love it as I did the day I bought it! I have taken several classes with this wonderful instructor and trust me.....if you know anyone that is like I was (intimated, etc. with guns) and wants to be comfortable and confident....he/she needs to take a very hands on course with an excellent instructor!
I believe if my husband and this instructor had started me with a 45 or something larger than the 9, than I may not have taken to it as well because of the recoil, etc. etc.
Let us know what you decide.