I have the Fein Turbo II, and recommend it. It is a bypass style vac, so the stuff your sucking up, never goes by the motor, it gets its cooling elsewhere. Now, to empty it less, I picked up, Onieda's new plastic dust deputy (work related reason why I went plastic over metal), if your getting something like a deputy/clearview/Thein then your budget may have to be less. The Ridgids, have a lower pitch, then some of the old Craftsman's I have access to. The Ridgids are made by Emerson, where the Craftsman vacs have gone from Emerson, to Shop-vac, and supposably back to Emerson.
Fein came out with a new one, (variable suction for sanders) so you may be able to get a deal on the older one. As for Ridgid, personal opinion, look for one of the ones with SNR (serial noise reduction), it is supposed to be quieter. Then you will need the $20 Craftsman auto switch.