Fourteen is hands-down our favorite building in the Alligator Bayou section of Port Orleans Riverside. For us it is probably a matter of convenience and view. Since it is right next to the Sassagoula River, the views are quite lovely and even without the water view, there isn't a parking lot beside the building so the others views aren't of concrete. It is also within a short walking distance to main building with Sassagoula Floatworks and Food Factory the closest to building 14. I loved this for grabbing cups of coffee in the morning. The bus stop is also just a short walk away.
However, building 18 is also very similar to 14 (they are neighbors), but it is right next to the quiet pool. You could even have rooms with a view of the pool. One other quality of 18 is while the walk is a bit longer, we grew to appreciate the meandering paths that wound their way through bayou-type landscaping.
Of all 3 buildings, 15 is closest to the bus stop, but part of the building backs up to a parking lot. It actually sits behind buildings 14 and 18, so it is basically a smidge longer to the food court and quiet pool.
I usually try to mention all 3 buildings in our reservation because the more flexibility Disney has the more likely our request can be accommodated.