I played on Behemoth before transfers and the highest que was at 68 players. Character creation restrictions are almost always up on Behemoth. Also, goodluck if you plan to do Odin and Behemoth FATEs lol.
Also consider the population caps that were added to zones in the Oct 17th Hotfix as a more populated server has a higher chance of running into these caps.
EDIT: Naturally it won't be an issue 24/7 on even the most crowded server considering it was added just recently and nobody has really confirmed what the cap is and on the other hand even the lowest populated server might trigger the cap lockout during a Odin/Behemoth FATE.
Best of Luck in making your choice.
I get a regular queue on Balmung when I log in, but it takes like a minute to get logged in. It's really a non-issue.