Well, that's not the way it was scheduled on christmas for Mavs/Heat, Pistons/Heat. Also have to take into account dates and other things at those arenas.
I'd say Ben Wallace leaving the Pistons takes a siginificant amount of steam off the Heat/Pistons, as the Pistons drop a level or two without him on that team.
Heat/Bulls will be, and I think is, the big east match-up now. Why? The addition of Ben Wallace to the Bulls, the continuing development of Deng/Gordon/Hinrich/Nocioni/Duhon, along with the other guys they've added to only increase the level of Chicago from what they were before. Which, indeed, was a solid, scrappy two-way team.
Other than Mavs/Heat, Lakers/Heat is bigger. I'm definitely down for Lakers/Heat on christmas, that'll be a good game for sure. Heat are one of the teams I've liked for years, and absolutely love Wade alone, and I really like Kobe.