I chose Papa John's. Perhaps they're better in the UK than elsewhere, or perhaps everyone else is worse, but in my, and most of the people I know, opinion(s), Papa John's is the best place to go in the local area, and we have Pizza Hut's, Domino's, Papa John's, Rocket Pizza and Pizza Go-Go in the area (as well as the hundreds of small local stores, but I try to avoid those as much as possible - with the big chains, you know the food isn't high quality, but you also know it's legal).
Of course, that's just for delivery. If you wanna eat a pizza at a classy establishment, Pizza Express is an amazing place, don't let the tacky name fool ya, it's actually one of the better chain restaurants out there.