The JP server Tonberry specifically has a very large English-speaking population, as it's the server that a lot people in Oceania (Australia/New Zealand/South Pacific nations) decided to aim for. So that would probably be a good server to aim for (as Khorneflake said though, any of the JP servers would be ideal if you're after servers on a certain time zone, as they're all based on Japan Standard Time which is GMT+9 hours.).