I just leveled up a DRK and started running 8 and 24 man content. I'm just wondering how we decide who main tanks when there are multiple tanks, but only one boss. In 24 mans, it looks like it's always group A's tank unless there is a discussion beforehand (like group A's tank is undergeared and asks to pass on main tanking).

For 8 man content, I've just stood there for around 10 seconds to see if the other tank goes, then I go main tank if we are still standing there.

When there are two different tank classes in the dungeon, does one take priority as main tank, like PLD > DRK > WAR, mostly because war can dps so well?

It also seems like the top geared tanks never want to tank. I'm assuming this is because they can put out a lot more dps, so the lesser geared tank should be the one focused on tanking?

In short, is there an etiquette for choosing the main tank so that I don't have to sit there waiting to see if the other tank wants to?