Yeah, I think it would depend on the situation and how close "close" is.
In many situations, and with unarmored opponents, I'd take a reliable semi-auto 12 gauge with 00 Buck for maximum stopping power and hit probability. (I know that shotguns need to be aimed, but I still think they're easiest long arm to quickly hit with.) The MP5 would be a better choice if collateral damage was a serious possibility.
If I was up against opponents wearing body armor, I think I'd take the G3 or one of the assault rifles with steel core ammo. The speed of handling wouldn't be the best, but penetration capability would become too important to ignore.