When my family stayed at POR, we had great luck with buses - we never waited more than 10 minutes for one. We used the South Depot (the one near the main, Check-in/Food Court building) exclusively, and it appeared to us that there were some advantages to doing so, in that buses seemed to stop there first, and only continued around the loop to other depots until they were full. If that meant they were full after the South Depot, they left without going anywhere else. (Perhaps there are other buses that stop at other depots first, but if they do, they must not continue around to the South depot -- we never had a bus pull up with people already on it.)