Your question might be better placed in the table-routing section, but . . .
You want your table to be stable and sag-free, along with having a very smooth surface. Many of the commercial tables use thick or laminated MDF with a Melamine surface. Personally, I like Phenolic plywood, but finding pieces wide enough for a one-piece top is a problem. (Woodcraft, for example, sells only 1/4 sheets, 24x48) You might also consider MDF or Baltic Birch ply, laminated to at least 1 1/2" with a Formica surface.