So after years of trial and error, I think I've discovered the right way to reheat cold pizza.
My main issue has always been with the crust: after reheating in the oven, microwave, toaster oven, etc, it's always been limp and saggy (ok for rolling up into a pizzarito, but not much else).
So my solution to that? Put a baking sheet into a cold oven. Turn it up to 400, let it come up to temperature. Put pizza on pan, let it go for about 10 minutes. Take the pan out of the oven, let it sit for a couple minutes. Remove to plate. Crispy bottom, melted cheese.
Perfect reheated pizza.