Pop Century in a heartbeat. Why??? Because although it is a huge resort, there are plenty of buses. There are lines for each park...no pushing and shoving when the bus comes...it's all very orderly.
Then, once you are on that bus, you go right to the parks. No stopping at other resorts, or at other bus stops within your resort. CSR has multiple stops within the resort, which adds time to your total trip.
So, based soley on transportation, Pop is the best choice. But, remember, if you leave the parks at closing, you will have a ton of company heading back to Pop.