Thor would win rather easily. No lantern would be much of a threat to the God of Thunder. Look at it this way Doomsday took on the entire Green Lantern Corps before he was defeated. Thor may not have the ability to come back from death the way Doomsday can, but he is certainly close if not even with Doomsday in terms of overall power. What he lacks in durability in the Doomsday comparison he more than makes up for in his battle skill, magic abilities, and warrior spirit. Sinestro's only hope for surviving this battle is not to fight it.