Honestly, go to a range and hold every gun you might like. Once you find the ones that are comfortable for you to hold, rent those and shoot them to find which ones you still like decide from there.
http://www.cnn.com/2012/07/20/us/colorado-theater-shooting/index.html?hpt=hp_t1
Youngest was a 3 month old. So far reports are saying it was a single shooter. He used teargas or a smoke nade. Also he had a pistol,shotgun, and a rifle.