People are saying there are more options for pizza toppings, but I dunno
Ketchup
Mayo
Mustard
1000 island
ranch
BBQ Sauce
Relish
bacon
Chili
Avocado
Lettuce
Onions
Cheese
mushrooms
eggs
peppers
on and on
And a couple other related points in favor of burgers.
- Pizza only really takes certain kinds of cheeses. "4 cheese" is about as crazy as it gets. It's mozzarella and various other mozzarella-like cheeses. With burgers, you pretty much have the entire cheese catalog to put on your burger. Want some American, Cheddar, Brie, Blue Cheese, Queso? OK!
- With pizza, you can only put 3 maybe 4 different toppings max before it stops being able to hold up. And if you go to Italy, the home of the pizza, they will laugh at you for putting more than 2. Burgers can hold much more. Want bacon, 1000 Island, lettuce, tomato, onions, mushrooms, and cheese on your burger? Sure thing!
Conclusion: Burgers are much more versatile in terms of toppings/variations.