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The queen bed is two single beds pushed together. I would think you get more space from having the queen.
What ever the bed configuration is when you arrive it can easily be changed by the cabin steward before your first night. Personally I find the 2 single beds layout gives more usable space down the centre of the two beds rather than half the space either side of the queen layout. Also you don't say whether you have an inside or outside cabin. The position of the window may also dictate your preference for bed layout.