I prefer mdf to ply for tops. Ply can have tension in it. Either one should be attached to a sub frame with cross pieces (like a floor joist system). No panel board is designed to stay level across a span. I've seen a lot of members have issues with warping when trying to laminate 2 layers together and I've never seen anyone have issues with one layer and a cross membered frame. I built one table with 5/8 melamine coated particle board and then I cut 3/8 deep grooves in it for t track and still had no problems but I made sure the grooves were very close or directly over the cross members. Using more material is usually not a good substitute for proper engineering to start with.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.