My latest and likely last loading bench has 4x4 legs, 2x4 framework at the top and bottom with three pieces of 1/2" OSB topped by a piece of MDF all glued together and screwed to the top frame. My presses are mounted on pieces of 1x8 oak bolted to bench top with the grain running front to back to prevent warping or breaking the top. A coat of polyurethane on the top was all the finish applied. Another piece of 1/2" OSB is screwed to the top of the bottom frame to form a shelf and stiffen the structure, along with 1/2" OSB on both ends to prevent racking. I'm not much of a woodworker, but figure that heavy and stout is always better than light and svelte. It's the best bench I've had, and after seeing benches with light 3/4" plywood tops I wonder how they don't break or bend when a heavy duty press is installed and used for sizing or forming large cases.
For loading at the range I use a piece of 3/4 marine plywood that can be clamped to a table and works well for sizing BR and live varmint cases, so a well braced bench top of 3/4 marine (no voids in the plies) plywood would likely work for me as a bench top, but OSB and MDF are much less expensive and easier to obtain not to mention no chance of splintering.
Even with the price of wood products anymore if a guy has minimal woodworking skills and tools I think that he could build a stronger bench the exact size he needs or wants for less money.