Reasons I’d go with the Mavs:

1) Shaq. Say the Mavs trot out a starting five of Dirk Nowitzki, Josh Howard, Jerry Stackhouse, Jason Terry, and Devin Harris. Who is Shaq going to guard? If they try this, and I’m almost sure we’ll see it at some point, and the Mavs get hot and hit a few shots in a row, can they force the Heat to play major minutes without their best player on the floor? See Shaq, Part II, below.
2) Versatility, This is the beauty of the Mavs. If they need to go big, they’ve got Erick Dampier and Gana Diop to guard Shaq. I’m not saying they’ll look him up or anything, but… that’s a reasonable two-some at the 5-spot. The Heat are who they are, and they’re not going to change their game much. The Mavericks have the luxury of trying things out, seeing what’s working, and going with whatever’s working best.
3) Avery Johnson, It seems pretty common to assume that Pat Riley can rely on his previous championship experience here, giving the Heat an edge in the coaching department, but… I’m going the other way. This goes along with #2. The game now is not the same game at which Pat Riley excelled, and Avery Johnson is at the very forefront of the revolution. I don’t think the Heat are going to have the ability to adapt to the different things the Mavs can throw at them. They have a structured rotation of guys, and no one on the bench who can really come in and change the game or the tempo with their presence.
4) Depth. They have it. Miami does not. And both teams have been playing basketball for a looooong time now. Legs are important.
5) Antoine Walker and Jason Williams. Okay, this one’s more personal than it is an actual reason. But I don’t want either of these two bastards to have a ring. Surely, each of them would wear it everywhere they want, believing that they were the reason that the Heat won. This is the same child who, a year ago, was taking a pen out of a writer’s hand and saying, “You ain’t writin’ nothin’, homeboy.” And he could get a ring? I can’t accept that. I just don’t want a volume shooter and a homeboy-pen-stealer to have championships. That would bother me.

Reasons I’d go with the Heat:

1) Shaq, Part II. Of course, there’s an opposite side to this. If the Mavs roll with the afore-mentioned unit of five, how do they defend Shaq? Probably with Dirk behind him, standing there and not moving, hoping to avoid foul trouble, with a quick double team coming and trying to pressure Shaq into getting rid of the ball, or stripping him. We shall see.
2) Tight Defense. The Heat played outstanding defense in the Detroit series (though I’d still contend that the Pistons made it pretty easy on them). Detroit had to work to get open shots, and Miami kept the lane pretty much sealed off. Their rotations are good, they’re quick to close out on shooters, and everyone appears to be buying into a defensive commitment.
3) Erick Dampier. For whatever the reasons, it’s a personal hobby of Shaq’s to abuse Erick Dampier. I don’t know why but Shaq seems to really loathe the guy… he called him soft, said he played “like Erick Dampier” after a bad game, and said that the only league Dampier could dominate would be the WNBA. I believe he sometimes also closes his eyes and pictures Erick Dampier when banging groupies on the road. Shaq’s hatred of Erick Dampier should be good for at least one win in the series.

Who I’m going with:

Mavs in five.