Not exactly a matter of conjecture...
Kind of a weird fight here- cause they've fought for real in the comics about what, a million times? Iron Man has (obviously) won every "war" these two have fought (even if he has lost a few of the battles on the way). Mandarin has everything it takes to match Tony- the tech, the smarts, the money... but it comes down to power. His rings are awesome, but Starks armor/inventiveness always gives him the edge.