Shelly:
Our family enjoyed staying at Port Orleans Riverside a few years back--the lush landscape and boat to Downtown Disney made it seem more like a Deluxe than a Moderate hotel!
There are four bus stops at Port Orleans Riverside, and none is more than three or four minutes from your room, so if that is your #1 reason for choosing a building, I think you'll be happy whereever you bunk! In addition, the closest buildings to the main building are 14, 15, and 18 if you're in Alligator Bayou and Magnolia Terrace if you're in Magnolia Bend. We enjoyed being closer to the "hub" than the pool.
We did request a specific building (18, I believe), but we were there during Value Season. Keep in mind that you'll be visiting when crowds are a little higher and room requests can't always be guaranteed.
For some other thoughts on favorite buildings
click here for an answer I gave not too long ago to a Port Orleans visitor!
Wishing you a magical vacation!
Whitney