Ok... having been a cop, worked corrections and been a firearms instructor I'll tell you now, do not buy anything.
As many (LOTS of very good advice from this group) have said, get training and try out several things. I've packed a S&W Mod. 29 .44 with a 6.5 barrel as well as a tiny .22 - it was all about my situation then and what worked best for me and the conditions. Right now I've got a custom .45 auto with a custom holster that's not light but is very good for what I want/need and I have three variations in the gun safe.
You will be different.
You will also need to confront what violence is all about. It's not like the movies or books and being involved in a shooting is very traumatic. Before ever making the decision to carry, you need to make a lot of very personal moral and ethical decisions and what it will all mean to you and the people in your life. Go talk to your spiritual advisor, Rabbi, Priest or whatever, talk to those in your life who may have to also deal with the decisions you make and really be sure you've thought this out completely.
Once you are really sure, get some trusted and experienced advice - seek out a friend or link through friendships to someone trustworthy who has experience with this topic - not a gun-shop-guru or mall ninja but a working cop (lots of federal agents come to mind) or someone with several years of firearm concealed carry to provide you some feedback and advice. Then you will be prepared to make some choices on what to carry... not until.
Paul -