Make it heavy, solid and flat. The heavier a bench is, the more I like it (until I need to move it over 5").

Mine is 3/4" MDF with a 1/2" thick tempered glass top. I have no idea how much it weighs, but if it were a couple hundred pounds heavier I'd like it better. Seriously.

A heavy bench doesn't move when you're sanding and cutting. Also, never cut directly on your bench top. Use a cutting mat from Wal-Mart or cut up a box and get some cardboard to cut on.

Flat is extremely important for reasons already mentioned.

Workbenches and Building Surfaces