I just really like the Shotgun. I know I find myself using the Magnum more, but I don't want that to influence my choice because of how powerful it is. I like the Shotgun, it has tons of ammo, and I like getting up close and personal to kill the opponents. It's also pretty useful against the Flood in the Campaign. Actually if anything, I mostly go with a shotgun and Magnum combination, so I can deal with guys from up close and from a distance.