I have stayed at all three . . . . .
My picks would be
Bally's (north tower)
Flamingo (ask for a room near the elevator)
Imperial (would never stay again)
My room at Bally's was very nice and I enjoyed my stay. I could see the belligo fountains from the window at the elevator.
I also liked the Flamingo, I stayed in a regular room I thought it was a little worn but fine (I've heard a lot of great things about go rooms). The grounds at the Flamingo are nice with fish, birds etc. And if you like history their is a statue of bugsey seigel and some say he is still on the property! The pools are very nice!
The Imperial Palace I would never stay again. I had the worst experience. (I know some rooms are better than others) I got a bad room that was some old room that looked out to an alley? In the morning the fire alarm went off and we looked out the door and the maid was running with her cart! Then I went too the spa and were told we would have to take the stairs because their was a fire in the elevator and all the elevators shut down. So, after all this I was tired and I thought I would go back to the room and take a nap! I laid down and as soon as I shut my eyes a a jack hammer was directly above the room!!! I called the front desk to complain but no one ever answered!
Have a great trip
Dena