If we're talking riots, looters, and gang members I would have to go with my AR - 15 (M4 type). Over penetration could probably be an issue but...
- It looks MEAN, so theres a little more psych. effect on an angry mob or gang
- High capacity mags are a plus for obvious reasons
- Ammo is relativly cheap and 5.56 NATO should be available
- Easy to maintain and repair if needed... rugged
- good accuracy within a few hundred yds
- M4 type is also good for CQB.
- Flashlight and other attatchments would be handy.
Anyway, thats my 2 cents! Second in line would be my 10/22