What Tanks Do You Consider A Threat?

ARGO: When you are sitting awaiting a battle and your pondering over the team screen, What tanks do you say to yourself "This tank needs to be taken out 1st". Everyone seems to have a different opinion on whats a threat and whats not and sometimes that opinion can change mid battle too. Well anyways I have noticed a few players go running directly at the biggest tank they see only to be eaten alive by mediums and lights....So, Is it the Superheavies? The Scouts? The TDs? What tank in your opinion truly is "The first threat" and why?
I ask that this thread be devoid of any and all arty discussion. It is targeted at Tanks/TDs only.