When TBC first came out druids were the absolute best tanks due to high threat generation. Then a few weeks later Blizzard bug fixed them. People started noticing how crazy good Paladin tanks were, but not right away (Paladin tanks needed some gear, they couldn't just walk into Ramparts with the pre-TBC stuff).

The point is, its impossible to say now who will be the best for level 80 heroics, and we will not know until a few weeks/months after WOTLK is out. Maybe that 1 single 100 badge level 80 item will make one class way better. Maybe the right combo of talent and profession will make another better.

And as pointed out, the best for heroics is not necessarily the same as the best for multiboxers. We want something with high threat and little micromanagement - warriors can make awesome tanks, but they are far from ideal for multiboxers due to the micromanagement required.

Me personally, I have a 70 paladin, 70 warrior, leveling a druid, and then gonna level a DK when wotlk is out. That way, no matter who the best is, I'll be ready