We requested the main buidling as we wanted to be near to the main pool and lazy river. Also we wanted to feel like we were in a hotel. We loved being in the main buidling as its close to everything, kids club, computer room, shop etc. Also we didn't want to be on a high floor as I was worried about my son being on the balcony, the main buidlin only had 3 storeys (i think). I wasn't bothered about the fireworks. I think you have to be on about floor 6 to see them. I would say that buildings 2 & 3 were also good locations.
Hope this helps.