If you're looking for a big delicious slice of pizza, you're better off going to where they do it best: Ian's.
PDR is basically the same concept as Ian's, the Madison staple that is a MUST try for any out-of-towners. PDR's pizza is the same size and about the same price, but it's not nearly as flavorful. Every time I've gotten a slice here, it's been dry and bland. The staff is average--I've really only ever been super impressed by friendliness and helpfulness of the staff one time. At certain times though, they'll give you free samples of whatever the chef is currently working on, which is a nice little "appetizer" while you're waiting for your pizza to be done.
PDR has recently become the "hipster" place to go (I guess Ian's is becoming too "mainstream"), but I'd still gladly wait in the line running out of the Ian's door if I had the time. If you're dining with a group, you'll find more seating here than at the Frances St. Ian's, but the State St. Ian's is better than PDR for large groups because you can actually all sit at one table (here they just have a lot of 4-seater booths).