I think the price is really going to be a factor when it comes to finding a good functional vac that's also relatively quiet. I've seen some shop vacs at a few shop tool stores were asking $200-$300 for them...and they really don't seem to be all that big either.
Some time ago when I was referbishing my first vehicle, I went out and bought a ShopVac brand unit for $80 - I think it was a ten gallon unit. Having been use to the regular house vacs power, I was really surprised. What a value I felt. But yes it was loud. You can however purchase an exhaust muffler or make one yourself - I did using PVC pieces and works on the principle of baffle and sound absorbtion. Until then I just put in some ear plugs and went to work.
I know use this same vac with a cleanable filter for cleaning up the shop, on the portible table saw, and other chores. I only wish it had a larger dia. hose to help reduce lodging of debri.
I think I've owned this unit for some 10-12 years now.