it allways depends on the Monster. while challenger is good on Monsters that are often in ragemode (jho, giginox,...) it isn't as good on monsters that are rarely enraged. so for a general set i might preferre AUL. depending on how difficult it would be to make them you could still make both and use challenger on easily enraged monsters and AUL on others
EDIT: Challenger gives you AUL and Critical eye+3 (+30% Affinity) so all in all about double the bonus of AUL (allways depends on how much atk the weapon has)