I really enjoy using the sniper, M1 and other "long-range" guns for room clearing, at least on first two levels (my regular haunts). I tend to do better with automatic weapons vs. bosses, really not even sure how much damage the sniper-type guns normally deal out to bosses.
Snipers are very good on bosses, but it all comes down to how good you feel your aim is with those weapons. Some bosses have patterns that are too hectic to take snipes at them reliably so automatic weapons are probably the way to go with those.