If money was no problem I'd buy one of each. A SCAR was mentioned in a YouTube video as a SD weapon but they ain't cheap. I have an AR but I'm not too familiar with the AK or shotguns. Some AK's seem to be chambered in 5.56 so that's a plus but I've heard that they can over penetrate. But, a shotgun is considered a good SD weapon since they don't tend to over penetrate. And then what to buy for optics, lights, etc........