After trying to create a character for my wife on Balmung to join me, I can say it's not "one of" the most populated servers but "the" most populated server. So if you want to get on Balmung you're going to most likely have to wait until before a maintenance/patch as this will be a time when there are less people concurrently logging into the game. Otherwise the other option is to create a character on any server, then pay $18 to get it transferred to Balmung in about 5 minutes. I tried for 3 weeks staying up late and waking up early to see if Balmung would open up and it never did. So I finally just paid the $18 and transferred my wife's character to Balmung and it worked within 5 minutes.