I'd go with B, if there is such a thing as "morally superior" his acts would be in this case.
Although just to clarify, I am religious but I dont do the "right thing" because i'm afraid of going to hell, but because its the right thing to do.
There may be a lot of people who have similar thinking as person "A" in this example but were not all like that. If God literally spoke to me now and told me there is no hell or heaven and we all disappeared when we die, I'm not going to stop believing him or thanking him for giving me the chance to exist.
And I'm not going to wildly try to satisfy all my carnal desires just because there's no afterlife, like everyone in movies seems to conclude is the best idea when the world is about to end ;)