Since I tend to travel along or with one other person and always book early and reserve my seat in advance then a 2-5-2 without a doubt. I used to be a fan of the 3-3-3 but travelling alone on a crowded plane with a window seat climbing over two people during a night flight when they are asleep. Terrible.
The best would be a 2-4-3 arrangement which caters for most party sizes and would keep the most people happy. Finnair I think it is has a similar config on their MD
-11, so why does nobody give it a go on the 777 - is it just because it looks too messy???