Here's my random comments on what previous posters have said:
School Pizza- Growing up in Allen Park, Michigan we had outstanding pizza at school until about 1984, when they switched over to cardboard crust, ketchup sauce and tasteless cheese that's typical of most school pizzas evidently. But the pre-1984 pizza was as good as any I've had anywhere. I am not kidding.
St. Louis pizza - I've tried Imo's and while it's not inedible, it's a ripoff and I don't even consider it real pizza. You pay $15 for what's basically cheese on a cracker. If Imo's is the best they've got, I feel sorry for St. Louis.
Peter Piper pizza - I've seen Peter Pipers around Phoenix and Scottsdale, but never tried it. It doesn't suprise me that it's not good. Everthing about it just screams "Cheap pizza for white trash!"
Little Caesar's - Don't know why some of you dis this place. I find it to be pretty good for only $5 for a large pizza that you have to wait two seconds for. Probably my favorite of the big chains. I'll take it any day over Domino's!
By the way, Domino's is pretty pathetic. I ordered their Brooklyn pizza one day because I had a coupon and figured, how bad can it be? It was ten bucks wasted. It was about as Brooklyn as a pizza made in Korea.
My worst pizza vote would go to CiCi's in the Kansas City area. It's a buffet, someone mentioned it here, it's garbage.