Verified answer

It would be quite difficult. Your plot would definitely have to be extremely strong and the characters themselves not cliche. It also depends on how you define "demon". Would they be demons in the Biblical sense, as in creatures that live in hell and can possess people, or would they be some other type of demon? Would they be the same kind? Would one be trying to be good while the other doesn't? That last kind has most definitely been played out to beyond its death.

Interesting....

I think it might make for a neat allegory. Perhaps a scenario where one nations plays two weaker nations against each other. Or a cold war allegory where the person was represented by some third world dictatorship and the two demons were the U.S. and Soviet Union.

Another good conflict might be a young woman forced into prostitution. She can face the horrors of selling her body or numb herself with drugs. Which demon does she embrace?

Use your imagination. Make the demons and mortal represent something.