Here's my take on it:
Battle one: Mistborn has Atium. Result: Dagger through the eye slit. (Note: All further battles will ban the use of Atium)
Battle two: Mistborn does an ambush. Radiant doesn't have Plate on. Result: Coin!
Battle three: Mistborn does an ambush. Radiant does have Plate on. Result 1: Well-aimed coin! Result 2 (Much more likely): Dink. Shardblade!
Battle four: Radiant does an ambush. Result: Shardblade!
Battle five: Head-on battle with preparation. Result: Mistborn uses duralumin + steel to crack Plate, while using pewter and/or steel to stay away from Radiant. Plate eventually becomes dead weight. If Radiant can dismiss Plate, coin. If not, dagger through the eye slit while staying away from shardblade.
Battle six: Head-on battle without preparation. Result: Mistborn Steelpushes upwards while Radiant runs out of stormlight, but must eventually come down. Shardblade likely follows.
Battle seven: Head-on battle with... Um... Intervention... Result: IT'S RAINING TACOS comes blaring out of invisible speakers at volume 17,000 while it starts raining tacos. Mistborn covers his/her ears and screams while running around in circles. Radiant goes flat on the ground, face-down, and bangs his/her head on the ground while shouting, "MAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOPMAKEITSTOP" at the top of his/her lungs. If Radiant is Lift, infinite Awesomeness! (Note: this battle was written by my brother and will not be taken seriously.)
REAL Battle seven: Mistborn attempts ambush, but is spotted by spren. Result: Radiant reacts enough that Mistborn realizes ambush has failed. Mistborn Steelpushes upwards while duralumin-Steelpushing coins at Radiant. Likely similar to Battle five.
Final score: Mistborn wins, 4-3