Donato's is slightly better than Papa John's, but both are pretty good by chain pizza standards. Here's how I rank them:
Donato's - The best. Don't have it as often as I'd like due to price.
Marco's - A very good, and significantly cheaper alternative.
Papa John's - A very small step down, but still very good pizza.
Domino's - The changes they made a few years ago helped greatly (old recipe was inedible).
Giorgio's - A little blander than the first four, but still best option for "hot and ready" pies.
Little Caesars - Another good option, especially if you don't want to order. "Detroit style" deep dish is awesome.
Pizza Hut - If you can get a good deal, avoid the pan crust, don't buy any sides (too little food for the money), and just order enough for that meal (doesn't hold up well cold), Pizza Hut can be a good option.
Did I miss anybody in regards to national chains?