I always break pizza cutters. I use a sandwich knife with a 12" blade.
I wouldn't mind one of those cutters they use at pizza places.
If you do ever buy a guillotine cutter, be prepared to spend a good amount of cash. It cheap
one will still run $50-$70 and will be a total waste of money. The unusual curve of the blade make them very difficult to keep honed. Cheap metals pretty make it impossible.
I've bought a couple at that price range, and they were both terrible.
I later bought one that was close to $200 and still use it. It cuts pizza like butter.