The little two letter word behind a server is meaningless. JP/NA/EU simply means nothing more than that the server is physically located in either Japan or in America.
All servers have equal amounts of JP/NA/EU players. I really wish they didnt put it behind every server, due to people thinking it's a server just for JP, or just for NA or just for EU... it's not... And the next person who says it is i shall pummel into the next Umbral Era personally.
Go join whatever server you like. They're all the same. Simply ignore SE's ill-choiced labeling, without actually explaining what it stands for.