Most of the west Anglesey campsites can be rowdy as it is the main destination for the tourists. Unfortunately, due to the islands proximity to certain northern cities, it does attract a certain type of inner city camper that arrive with a festival tent, a very loud stereo and 400 cans of Stella. Definately to be avoided during Bank Holiday weekends at the very least.
Try TyHen at Rhosneiger (if you can get in - book early) or the other one near the lake there whose name escapes me at present.
My advice would be to go north to some of the little farm campsites if you are looking for unspoilt beauty and a peaceful break.