The guy holding the belt is the best fighter in the world. You can argue otherwise, but that is only spaculation and subjective thinking, so from what we know, the champ in each division is the best fighter.
Seems like there are only two weightclasses where guys think the champ is the best fighter (at the moment I am writing this), and that is BW and LW. That is just fans speculating...
You could argue Jones DC...