So you've managed—by some divine grace—not to finish your entire pizza. That alone is an accomplishment, and you should be proud of your restraint. After all, good things come to those that wait (there have been studies that prove it!).
What has not been studied enough, however, is the best way to reheat these glorious leftovers. The microwave, technical marvel that it is, will render your slice a soggy mess, with crust that's way too hot and mushy. (Really, if you're going to burn your mouth on anything, it should be the cheese.) The oven, while it restores the crispness that made you fall in love at first bite, will also dry out your cheese and toppings. No amount of crunchy base is going to make up for that failure.