While you might not share a bus, there is often standing room only on the POP buses b/c they fill. And, since it's a new resort (and popular b/c of that), the buses are crowded.
On our last trip we stayed at POP. While waiting for one POP bus to come, we always saw several All Star buses waiting or leaving for the resort. Often, we'd see two buses for movies getting ready to load. It was frustrating to wait for a single POP bus while all the All Star buses were passing us by! Also, on POP, we often had to stand b/c of so many passengers getting on. In the morning, they loaded the buses to capacity to go to the parks and people also stood. No seat guarantees at all at POP. Going back to the resort, same thing ... unless you wanted to wait for the next bus.
Honestly, as far as standing room goes, it depends on the crowds at your resort.
And, according to the WDW bus drivers, as they pull in they're instructed to go to stops based on need. So, if there's a crowd for All Stars and not for POP, they'll load up All Stars first and get them out of the way.