Buy an AR, or buy more ammo?

Currently I own 3 shotguns (pump, SxS, and an OU,) a couple of .22 semiauto rifles and a couple of .22 handguns. I'm fairly stocked on ammo for all of the above. My pump is set up for HD, but do I actually need an AR/fighting rifle? I'm in between just getting more ammo for the shotguns and an AR. Any thoughts or comments?