Which patch version of WoW would you play if you could?

Imagine when logging into World of Warcraft, you would have a screen on which you could select which patch version of WoW you wanted to play. On offer would be a late vanilla WoW version, a late Burning Crusade version, a late Wrath of the Lich King version, or the current Cataclysm version. Which of these would you play?

Now to completely change this discussion around, let's consider the high likelihood that you actually had an answer to my question. And that this answer isn't necessarily the

World of Warkraft...