@Cos is right, a pizza stone is great - so is a pizza screen in the oven.
If I don't want to heat up the oven (big oven, little piece of pizza aways seems like a waste), then a cast iron pan over medium heat on the stove with a lid does pretty well.
cooking.stackexchange.com/users/1374/rfusca
I have always had the most satisfactory results from preheating the oven to 400F with a pizza stone and then setting the cold pizza on the hot stone for 8 to 10 minutes?
cooking.stackexchange.com/users/6279/Cos Callis
If you just want to reheat a slice or two, you can warm it in the microwave for 30 seconds to a minute and then put it in a toaster oven on toast or a hot oven setting for a few minutes.
It's best in the toaster oven if you put the slice(s) on the broiling rack on top of the baking sheet.
cooking.stackexchange.com/users/839/Rebekah
Since I prefer thin crust pizzas, oven re-heating often results in something resembling a burnt cracker with some half-cold toppings on it.
To avoid this, I "fry" leftover pizza to reheat it: I place a tiny bit of oil or butter into the bottom of a non-stick skillet, add slices of pizza, cover, and place over very low heat until the cheese is re-melted.
This method allows the pizza to warm and steam gently, while also ever-so-slightly frying the bottom of the crust, so one ends up with something very near the consistency of a fresh slice rather than a dried-out, inconsistently-warmed leftover.
This technique works with everything from thin crust to deep-dish pizza; only the reheating times are different.
cooking.stackexchange.com/users/359/goblinbox
I like to put a heavy sheet pan in the oven and preheat it to 350°F.
Then I just slide my leftover slices onto the hot pan and bake for 5 minutes.
The hot pan crisps up the bottom of the crust and the hot oven does the rest.
Does a nice job of bringing a good slice of pizza back to life.
cooking.stackexchange.com/users/10360/Callithumpian
I found that a short burst in the microwave heats up up the whole piece.
Then, you have to immediately put it into a very hot oven to get it crispy on the outside.
(You said "the best way", not the most energy efficient.)
cooking.stackexchange.com/users/36444/Junco
I use an oven at 250°F for a longer period of time--usually about 15 minutes, with the pizza either in or on tin foil.
This seems to work well, it heats the pizza but doesn't toast the crust.
cooking.stackexchange.com/users/3310/philosodad
Pizza stone on 350 for 10 minutes.
Or if your lazy and don't own a pizza stone, like me, toaster oven on toast for however long it takes too heat, crisp up and not burn.
cooking.stackexchange.com/users/35726/jmuller
With a waffle iron!!!
Leftover Pizza + Waffle Iron
= Delicious Crispy, Gooey, Cheese-Stuffed Snack
cooking.stackexchange.com/users/8864/mike
For larger amounts of leftover frozen thin crust pizza-
Line a medium/large baking pan/sheet that has at least 1/4 inch vertical sides on it with tin foil.
Use middle rack.
If two baking pans are used, use rack positions 1 and 4. 1
being the lowest rack, 4 being the higher one.
Preheat oven on Convection/
Bake at 425F to 450F. After preheating oven, place frozen thin crust pizza on baking pan/s.
Put pan/s in oven and heat for approx 30 minutes.
Check at 20 minutes to make sure not to over cook.
Enjoy!
cooking.stackexchange.com/users/61590/Redbrddad
Whats the best way to reheat leftover pizza? We usually use Boboli Crust with our own toppings, or sometimes we have frozen pizza.
Best way to reheat pizza
cooking.stackexchange.com
<pizza><reheating>
cooking.stackexchange.com/questions/17192
cooking.stackexchange.com/users/7201/fuzzbone
A hot oven with a pizza stone for 8 to 10 minutes produces the best results, although you can also warm it in the microwave for 30 seconds to a minute first or fry it on low heat in a covered skillet. Try using a pizza stone, quickly reheating in a microwave or frying in a little oil.
Use a pizza stone for 10 minutes. Try microwaving or frying with a little oil. Try a waffle iron.