There's no way anyone can tell you the amount of NA versus JP players on a server. It's clear to say they were lying out of their ears. There's just no way to pinpoint the amount. And even then, those people have only ever been on one (or in worst case two) servers. They wouldnt be able to proclaim their server has the most NA players.
At best, they can say there's a decent amount of NA players online on their server. But that goes for just about any server.
You could probably, technically, find the amount of active accounts per server on FFXIAH, but that too wont tell you much. Can be that people simply have a lot of AH activity on a people with a lot of mule accounts.
Just pick a server who's name you like and go with that.