"Who will live longer" is basically the same as saying "Who will die first" which is the same as "who would win."
Unless you mean in survival years. Obi-wan died when he was about 52ish. Revan was, I can't say for sure, 30ish? If whatever happened to him in the Unknown Regions doesn't kill him, he might live longer than Obi.
Originally Posted by Darth Moeller
They would fight for all eternity until one of them died of extreme old age.
Well, I've got my vote on Obi-wan, since he Was born about 3,500 years after Revan likely died.