You are right to ask the question because although the layout of Summit is fine in general some of the balcony cabins are put in the shade by the overhanging structure of the Resort Deck and that makes the 2C grade better however if you value your privacy and want to sunbathe without being overlooked study the plan of the ship and try to pick cabins at the extremities. We always favour the ones on the rear of the ship as they are much larger than the rest but they are always the first to get booked. I hope that help.
The best rooms on Summit are 2C and rooms 6022-6030 and their mirrors on the other side = they have double depth balconies but this is a well kept secert! So don't tell anyone.