This isn't exactly a battle, as it is a race. They must race throguhout Jerusalem, as seen in Assassin's Creed. But they'll face opposition such as guards and seceral traps(nets, bear traps, dug-up grounds, etc.) When they finally get to the finish line(Top of Altair's headquarters), they'll have to battle each other.
I may be somewhat inclined to say Altair if a draw isn't possible, depending on, as Kazenji said, which character it is. After all, Altair's on his own turf :P.