What brand vacuum works best on shag carpeting?"

Any good vacuum will do the job as long as you can turn the beater bar off. Then again, it depends how long your shag is. Beater bars will help bring dirt and debris up from the base of the carpet so that your vacuum can remove it, getting your carpet much cleaner and prolonging its new appearance. If your shag is an 1" or less high, you should be able to use the regular "carpet" (or beater bar) setting. If it is higher than that and you just recently purchased it, contact the manufacturer (not the vendor) for maintenance guidelines. If you have a super-long shag, fibers can become tangled in the beater bar and harm your vacuum. Not all vacuums offer a "hard surface" setting. Dyson - a fabulous suction machine - does offer both carpet and hard surface settings and will clean your floors very, very well. If you have a vacuum that you like right now but it doesn't have such an option, you can use the hand attachment to vacuum an extra-long shag. Tedious, I know, but at least you can ...  more