If toilets are a concern, go for the upper deck. The toilets downstairs will usually have a few economy pax in line that simply pull the curtain aside that separates Y from C. Sometimes the FA enforces the rules, sometimes not. I prefer the UD, although usually not the exit row because of the draft as mentioned above.
Another handy benefit of the UD are the side bins on the window seats. Big enough to store a bag, the blanket, laptop, etc.
Service is the same, so more depending on the crew.