This thread seems to have strayed from 'most types at an airport' to, 'most types at an airshow'. Even if Oshkosh is considered to be an airport (moot), how many different types would you see there on a non-show day?
Maybe the thread should be re-titled, "Airfield with most diverse aircraft types", but this would/should still preclude airshows/displays/fly-ins etc or I'll go with Davis Monthan. If you include Pima and the surrounding yards I doubt you'd beat it, but it ain't an airport, and I suspect derelicts and museum pieces miss the remit as much as fly-in types and airshow one-offs.