If you are going to buy a vacuum, get one with a HEPA filter, or buy a HEPA filter to go in it. The regular vacuum filters just put a lot of tiny dust back into your shop air that you really shouldn't breathe. If you have the money, a vacuum with self-cleaning HEPA filters is the way to go. They really do maintain a lot more of the airflow over a longer time than non-self cleaning HEPA filter vacs do. Best bang for the buck right now is the Dewalt DWV010. That's what we are using in the metal area. It can be tool activated, but there's no variable suction, and it has a small canister, which is not a problem if you put a little cyclone inline ahead of it. If you really need wet pick-up, you'll want a bigger vac. Or get a cheap non-HEPA vac just for wet pick-up. Wet pick-up always makes such a mess of the vacuum.
FWIW we have the Dewalt DWV012, and self-cleaning HEPA vacs from Metabo and Makita in the wood area of the shop. Of these I like the Metabo best so far, because it is low and the 5 gallon bucket with the cyclone fits on top, next would be the Dewalt vacs
