Several option are available, depending on budget.
Aluminum is probably the most stable.
Phenolic is a standard option, and is what is on my Biesse Arrow.
Depending on if you can machine alum with that model, it may remove that option or require that it be machined prior to assembly, which is less than desirable.
Biesse's phenolic choice is probably pretty darn expensive, so if I were building from scratch I might consider something like "Paperstone", and counter-top material that is made from phenolic resins and recycled paper. Should be stable, at least reasonably, strong, modestly expensive, but not as bad as some options, and although a bit tougher on tools than mdf, you only have to machine in once for your application.
Have you seen their "universal" vacuum table grid pattern? I haven't measured mine in years, but I think it is a 30mm grid, with about 8 mm grooves, subtle air channels on the tops of the squares, plenum holes about every 8 inches or so.