I think FF13 would take it, but i dont actually know why....

I don't think the two have ever been involved in a "fair fight" to make that assertion. FF spent the last two generations prior to this one on a significantly larger userbase, but Zelda held it's own both generations in comparison to those titles. When they compete on the same platforms like the DS, SNES and GBA, there's always the factor of Nintendo titles having a significant edge against third party titles. Basically it's not easy to pick apart which is the bigger franchise when all is good in the neighborhood. I see them as equals. They are the start of the new level of secondary titles, now that 15 million is becoming more customary for top tier.

Well, how much would one expect them to sell?

Zelda first, as I have more of a clue there.

TP will end at ~ 7-7.5M. As this Zelda will be the second on the console, its sales could be lower. I doubt that, however, as the other was a launch title, and this one appears at the peak. Still, let's put 6M as the bottom. Now, for the peak. I'd estimate that a good 9M would be the highest.

So, a 6-9M for Zelda Wii.

Final Fantasy Xiii? It's kinda hard to tell, but let's say it keeps the GTA ratio from X/VC last gen. That's... 0.56. So it would lead to a roughly 6 (GTA IV current sales *0.55) to 8.8M (16M *0.55).

That was surprisingly close.

Which of the numbers do you disagree with?

Yeah.  Damn.

Well, in that case, I think the only fair fight would have to have been Link to the Past vs. Final Fantasy 6, in America alone.  They were both on the SNES, and they were both the 3rd major series home console release in America.  So I'm not counting Mystic Quest, FF2, FF3, FF5, or the handheld Legend and Adventure ones.

But our sales data doesn't go back that far, so I can't find out who won.  It will remain a mystery.

u get banned a lot :(