Is plywood fairly stable? I've built car audio speaker boxes out of MDF and it's pretty solid...
How about routing,does plywood route well? 
If it's sturdy.. holds screws.. and routes well.. don't see why not to go with it? (probalby cheaper too???)
MDF is stable because there is no wood grain to move. Plywood is practically as stable because of the alternating grain layers.
Plywood doesn't route as nicely as MDF but it should be more than adequate for your needs. If your routing because your putting plexi on top I would go with a thinner piece of board and avoid the routing.
Plywood is also not as smooth as MDF so it depends on what your planning to put over the control panel.
Plywood is stronger than MDF but in this application I think either would be strong enough.
Plywood will hold screws, MDF won't.
MDF is smoother than plywood. You can get plywood that is smoother (still not as smooth as MDF) but cost goes up. MDF is cheap compared to high quality plywood and about the same as cheap plywood.
Plywood is lighter than MDF, MDF is very dense
A lot of cabs use MDF for the cab and plywood for the control panel. Another common option is melamine. Melamine is sawdust board with a cheap protective colored film on it. Its not near as hard as formica. Its the stuff they use for closets and shelves, usually in white but many other colors can be ordered.