Lots of good advice here, including those recommending a revolver or a shotgun. Jim, myself and lots of other folks could write pages on why we think you'd like this or that. I think the best advice is to go to a shooting range and put a few guns in your hands, and then rent at least a few of them to try and see what you are most comfortable shooting. Many ranges will charge you a fee, say $10, to rent a handgun, and you can bring it back to them and switch it for another with no additional charge. If there is a charge, it won't be much. This type of experience is invaluable, what works for me might not work for you.
I will say IMHO don't get too wrapped up in the 'bigger is better' idea, as a newbie at least. I love larger caliber handguns and have a lot of experience with .40 and .45, but because of having neck fusion surgery a year ago and still not being up to full strength, the best caliber for me right now is 9mm. Why? Because after my first shot, I can return to point of aim faster on subsequent shots.