Good fight. I'd say Marvel's durable enough to endure Sinestro's attacks and the Courage of Achilles and Wisdom of Solomon should steel him from Sinestro trying to use his fears against him. Sinestro's infinitely more versatile, but Marvel's a physical powerhouse.
I personally give Marvel the slight edge. 6/10 for the World's Mightiest Mortal
I'd give a slight edge to Marvel as well, he does have an overall speed edge and would absolutely dominate a close quaters fight. At distance he's at a disadvantage but I don't see him giving Sinestro time to destroy him at range. More often than not his durability and speed give him the edge, if Sinestro can't put him down while he closes the distance, he's done.