It depends on what you want.
There are no bad buildings. All of them are within about a two-minute walk of the main pool and activities center.
You are correct; building 1 has no elevator and is the oldest building. Building 2 is probably the quietest - no adjacent pool or street. Closest to the beach, if you plan to walk, would be buildings 2 and 3. Closest to and partially overlooking the main pool is building 6. In April, you might prefer buildings 7 or 8, which are adjacent to the smaller (but heated!) pool. One advantage of the buildings closest to the activities center, the ability to - in some units - access a wireless Internet connection, has disappeared with the installation this past winter of wireless Internet service throughout the resort.
You can view a map of the resort on the TUG review page for Waterside. Click on "View All Images".