I would NOT purchase a vac sold at a store other than Lowes, Home Depot or Sears. If you need a replacement hose, filter, or other item, these stores have them and are open late night and on weekends. If you have an odd ball type vac, it will be harder to get these parts.
BTW, I like the shop vacs that have a water hose threaded nipple on the canister so that if large volumes of water need to be removed you can run a hose out the door rather than having to repeatedly empty the vacuum.