We have always requested the Sierra Tower because you can't get a bad view. You either get the swimming pool or Downtown Disney without having to pay for an upgraded "view" rate.
That is true, but bear in mind that many of the rooms in the Sierra Tower are upgraded view rooms. So that makes getting a room there on a standard rate not always easy to come by. Its also the most requested view.
Really and truly the only crummy views at the DLH are in the Bonita. Half that tower faces a parking lot. The other half has great views of the fountains,
Disneyland, the wedding pavillion (we once stood at our window and watched a very lovely wedding down below which was sort of neat) and the other towers depending on where you are located on that side. That happens to be my favorite tower to be in, IF I get that one side.
Oh, and that third Tower is called the Marina Tower. Its where the lobby/check in area and gift shop are. You can see the pool and park from one side with some nice views of the fireworks. You can also have a view of the parking lot but that also includes the Mickey statue. That parking lot view at the Marina is far better than the parking lot view in the Bonita.
Call the hotel, preferably the day of your check in, after 11:00 a.m. when everyone has checked out. That is when they will have a better idea of whats available for that day. Also, when you check in, the castmembers are usually happy to go over what they have available for you.
The only way to guarantee a good view in the end is to pay for it. But in six stays I have only gotten the Bonita parking lot view once. My first trip, when I didn't know enough to ask for something better that might have been available (pre disboards days obviously)!