[ZanooKu]

Alright so if it's not EMP Terran use to kill everything, It's Siege Mode.
I find early game they can have 1-2 which will stop any gateway units breaking in which brings me to mid game. Immortals have barely any range, and get chopped by Marines. Colossi cost more minerals/gas and supply. Are a higher tier and are more vulnerable to air units yet they have under half the range of a Siege Tank until upgraded which still has 4 less range. As the game goes on the tanks can slowly progress forward and use Medivacs for vision. Before I even get close to their units, they're already taking out at least half (if not more of my HP). This replay isn't the best example as I didn't get Immortals, but apart from that... well I'll just let you decide on how "balanced" tanks are...
http://www.sc2sea.com/downloads.php?do=file&id=95