The biggest difference between the seats is storage. All seats downstairs, and upstairs aisle seats have none. Upstairs window still has the small storage locker beside the seat that it did on the old config.

Climbing over the person to get out from an window/middle seat isn't difficult for most people.

Presuming you're not physically challenged in some way, I'd say upstairs window is the best. Otherwise they are all pretty much the same.