Assuming that the physics would take care of themselves, or that we'd have a tzar of constants who was superpowerful and not self-interested and could adjust things as necessary (i.e. the moon would not collide into San Francisco, etc.), then I'd like humans to have a lower gravitational constant than everything else.

This would make us all like John Carter. We could jump/fly many places which would reduce our transportation footprint, and hopefully we'd live longer as a result of our new, more active lifestyles. I also think it would be fun every day, and it would also be something of an equalizer across the world.