Hello Kristin! Welcome back to the Disney Parks Moms Panel.
Strolling through the recreated bayous of New Orleans and the relaxed atmosphere of the sprawling location makes
Disney's Port Orleans Resort - Riverside 1 of my favorite Walt Disney World Resorts.
While you are correct that the South Depot is (usually) the final stop that
Complimentary Disney Transportation makes before leaving for the Theme Parks, Water Parks and Disney Springs, I believe that the advantages of staying in a Preferred Room should outweigh the concern of full buses.
When my family stays at Disney's Port Orleans Resort - Riverside, we usually opt for a Royal Room located on Magnolia Terrace as close to the main Building as possible. This provides us a nice balance of closest proximity to the Main Building at Riverside,
Disney's Port Orleans Resort - French Quarter and Ol' Man Island Pool and Recreation Area.
In addition, it puts us in close proximity to the West Depot to ensure we jump on the Complimentary Resort Transportation before the South Depot bus stop. However, during our Walt Disney World Resort vacation, we never experienced an issue with overcrowding on buses even when we boarded at the South Depot.
With the benefits that come with a Preferred Room at Disney's Port Orleans Resort - Riverside, I recommend you keep the room. enjoy the close proximity to all of the Resort action and walk to either the West Depot (for Alligator Bayou Preferred Rooms) or East Depot (for Magnolia Terrace Preferred Rooms) during Peak times (morning, mostly) if you are worried about full buses.
Have a Good Ol' Time Down the Bayou!
~Todd