I have stayed in the North Tower with a partial view of the Bellagio fountains. If you would rather stay in a room with furniture and carpet over 20 years old and have a chance to see the fountains from your room instead of just venturing across the street to see them, stay in the South Tower. If a decent room is more important than the view, North Tower. I wouldn't stay in the South Tower for anything.
I will say this about having a room with a fountain view, several times I have stayed at Caesars with a Bellagio fountain view. But not once have I seen the fountains from my room after dark. I am never in my room between sundown and the time the fountains stop. So unless you hang out in your room in the evening, the fountain view really doesn't add all that much