I voted 3 (Rome, Venice and Milan) and will add Tuscany too. The problem is that the first 3 are riddled with tourists, especially during the summer season, so I would suggest you go in Autumn or Spring, you also avoid hot sticky weather that way.
Italian Pizzas are fantastic but don't order one with pepperoni as it doesn't exist there unless you find an American Pizzeria there. Pepperonis are an American invention/creation.An italian can confuse it with you ordering peperoncino which are thin red or green peppers and it has nothing to do with peperonis at all☺️