I have worked with surface plates for years, they are somewhat similar to a saw table top.
Durable, won't crack, will bend if it is thin, will dent, rusts, needs constant upkeep if not painted. If the steel rusts or gets dented, you will need to stone the top.
Durable, will crack if it is thin, will not bend, will chip if metal objects are dropped on it, will not rust, does not dent, easy to clean, less upkeep overall.
I would rather have granite, if I could afford it. Even if it chips, it will just make a little divot on the top, but it will still be usable. You never have to oil or wax a granite top either. Both are a pain to lap, steel tops can be taken to a machine shop. Granite could probably be taken to a place that manufactures surface plates, possibly Starrett(?), and they will be VERY costly. A calibration facility would only be able to take off a tenth at best. I doubt the home user would ever need a granite top lapped.
Last edited by cheese9988; 03-27-2010 at 02:52 AM.