Inside the ship
Northern Lights (the disco): Empty during the day. Booths with tables but can be a little dark.
Queens Lounge (the culinary arts center): If no events are scheduled it is usually empty and you have your choice of different seats .
Atrium bar (lowest level of the atrium): People pass through and are booking tours but they tend to walk on by the bar area.
Vista Lounge (the big theater at the bow): If nothing is scheduled there is a lot of room to find a quiet corner. The doors are closed when there are rehersals.
Out on deck
Middle of the observation deck (outside the sliding roof): There are no chairs but most people go to the bow or stern to gaze at the sea so it's usually quiet.
Lido deck forward (balcony in front of fitness room): Most people don't know how to get there. From the deck 9 forward stairwell, walk forward on the starboard side, keep walking past the fitness center to the end of the hall. Push the door hard, it has a strong spring.