My favorite is Magnolia Terrace (bldg 85). It's very close to the East Depot bus stop (which is way more quieter than the Main Bus Stop, way more isn't even strong enough to describe how much quieter it is - and this is a benefit). It is also very close to the pool and main building. It's just a bridge to the pool and then another bridge to the main bldg. I think it's the best location at the resort.
Also, if you requested a water view, you may want to specifically request a river view. You also may want a Mansion since most AB water view rooms are of a pool. There are some along the river, but i think the river is prettier by the Mansions. There are also pool view rooms in the Mansion, so when you check in, poliely say "I would really like a river view in Magnolia Terrace if possible" If they have it, they will (most likely) give it to you. If not, they will find a river view in another building. I have had no problems at POR getting what I asked for at check in.
Good luck deciding and have a great time. You'll love POR.