There might be a "least bad" pizza chain, but not a "best". Using the word "best" implies anyone of them are worth eating... and if you've never tried a small local pizza shop, you've never had good pizza.
But I will give CiCi's an honorable mention, simply for the $4 all you can eat smorgasbord.
But I will give CiCi's an honorable mention, simply for the $4 all you can eat smorgasbord.