I think it's just a matter of location mainly. There are probably more "noisy" rooms on deck 2, being that you have a lot of the night clubs above you in some sections. I have been on deck 2 twice. Enjoyed it very much both times. Very convient for getting to dinner and to the nighttime activities, also very convient to getting off the ship at port. It's just a walk of the stairs down to get off, and one flight up to eat and party!!
There are no verandah's on deck 2 though. Just outside and inside staterooms. The "noisy" rooms tend to be under wavebands. I had a "noisy" room on my last cruise, really wasn't too, too bad. Just the faint base sound--just note it does go on until 2am.
Deck 1 has been my personal fav so far. Quiet as a mouse down there. Also, just as easy to get off the ship, and still only 2 flights up to eat. Port holes are smaller on deck 1 (you actually get two small port holes rather then the one large one.)
But as far as size, all the outside staterooms are the same--regardless of which deck you are on. I think most people just prefer to be on decks a little higher.. especially families so they are near the pools and children areas.