Hi Melissa! Choosing the best resort for your needs is an important part of vacation planning for Walt Disney World.
All of the Disney moderate
Resorts will have internal bus systems as they are large and have many separate buildings. The only way to avoid this is to stay at one of the Deluxe Resorts or some of the Value which will have one main bus depot. Even when staying at those you might have a hike to get to that area.
My preferred moderate resort is Port Orleans or the Fort Wilderness Campgrounds which include those fun cabins you can reserve. They both have efficient internal bus systems and I enjoy the atmosphere better then other resorts. I don't feel like I have hundreds of other guests around me all the time and find the feeling very relaxing.
You can always note on your reservation that you would like a building close to the main bus area or a room and building close to a bus stop. Once you arrive see how the bus runs as sometimes we have found if we did not get off at a close by stop we ended up going through the entire resort before reaching the stop at our building. To save time it was worth a short walk back to our room.
It is hard to say one building is better then others at the Caribbean Beach or the other resorts. One building will put you near the bus that stops first but then you have to take the route through the resort to pick up other guests. Then you can choose the building where the bus stops last and by that time during busy months you won't find a seat and the bus will already be very crowded. So you see it is best to just pick the resort of your choice and request near the pool, check-in building, or a bus stop and enjoy the amenities as best as you can.