Here we go again........
Skill-wise i'm 90% sure it's EU. I've played on both for ages and the average level of skill, as well as the top level just seems to be lower on NA (there are a few exceptions to this). Which community is larger, more fun or friendly I'm not sure as it's harder to be part of a NA community when you're barely on at that time. Ironically the best NA player I ever fought was Jackie (on both EU and NA), and he was originally an EU player.