Center cockpit you sway to and fro more then the lower, aft cockpit. Spills drinks.
The Oceans is mainly a 'cruising' sailboat whereas the First series is the 'racing' boat. I didn't realize how drastic the difference is until I saw one of each side-by-side in a marina. the Oceanis was 18 to 20 inches wider to provide more room inside. The Firsts can have nice interiors, though. I have a 323, and as any owner will tell you, they can move pretty well.