There are sealed freewheels (WI, token, profile) and unsealed ones (dicta, shimano, halo, acs, etc.) The unsealed ones will all die if used in crappy weather (~1-2 years commuting) crap gets inside and the ball bearings start to wear faster, it becomes loose or the pawls stop catching or similar. Adding oil can extend their lives a bit. The WI ones are great but a bit of a false economy as you can buy 10 dicta type freewheels for one WI one, and the WI casing is quite expensive compared to the cost of a new WI freewheel (and the last time I did that I found they now only sell the new casing with a new bearing).
Get one that works with the standard 4 sprog removal tool.