I am getting ready to make a new wasteboard system…a permanent panel with t nuts installed, and then replaceable wasteboard panel on top of that. I have MDF on hand, but is there any reason to believe 3/4 ply would be a better/more durable material to use for the bottom panel that holds all the t nuts?
I have had issues in the past with the MDF holding helical threaded inserts but you are probably fine with t-nuts.
Plywood would be more resistant to moisture.
The benefit of MDF is it’s a single piece of semi-solid material that can be easily milled and maintained through multiple surfacing operations. Plywood, unless you use expensive Baltic birch plywood, often has voids in its layers, the layers are uneven and patched, and overall, the plywood is not as flat. I wouldn’t go there.