As of 2014, the Papa John's large pizza is 14 inches and the medium is 12 inches. They have a special running for 2 large or 3 medium, and if you're only concerned about the size without the crust that is ~11 inches diameter for the medium or ~13 in for the large.
3 medium = 3 x 95.03 = 285.09 sq. in.
2 large = 2 x 132.73 = 265.46 sq. in.
So, the medium is the better deal for the same price. However, the large special included a specialty pizza, so that's what I got.