On the Magic it's deck 1. We've only ever sailed on the Wonder (decks 5 and 7) and the Magic (deck 1). We were in 1079 for 21 days this summer and it was perfect. The motion is gentle down there.
For us, we only used the stairs. We had our 8 year old daughters with us and were going to be onboard for so long that we didn't want to gain weight. So no elevators for us. We went up and down so much it was amazing. But we also ate whatever we wanted and managed to still fit into our clothes at the end of the trip.
We are hoping to take a trip next year and have reserved the same room. We were right by the doors to the crew area, so it was blissfully quiet there. Actually, that's not entirely true. It was blissfully quiet on the EBTA, but on the Med we had the most obnoxious family across from us with horribly loud children running up and down the halls at all hours while yelling. But we figure that could happen anywhere on hte boat.
We did talk to others who said that being on that level made getting an elevator easy.