What type of fights should a beltholder take?

Once you get that belt, YOU GO UP IN WEIGHT AND CONQUER THE NEXT DIVISION AND SO ON. Like Conor did. THEN ONCE YOU CONQUER YOUR SPORT, YOU GO AND TAKE OVER ANOTHER SPORT.

Ideally they look to unify the belts, or at least take on the best fighters available between mandatory obligations. There's no point in calling yourself a champion if you're not facing good competition. Obviously we know it doesn't work this way.

I think a new champion should stay in his own weight class unless he is young and outgrowing that weight class. Nobody likes catchweight fights and fighting above your best fighting weight is a good way to lose when nobody can beat you at your best fighting weight. Look what happened to excellent boxers Donaire and Gonzalez when they moved up too many weight classes to fight bigger, stronger, harder hitting men.

A confident new champion who believes he can beat any boxer in his weight class would be doing 1,2,3 and 4. He would want to fight the best and highest rated fighters in his weight class that he could get a fight with. He would want to beat the other champs in his weight class to prove he is the best at that weight. He would want to get high paying fights but usually fighting the best boxers or the other champs makes him the most money anyway. He has to fight his mandatory challenger before the deadline to keep his title. Fighting the fighter he has the biggest grudge against is not what a good new champion should do unless that fighter is a high ranked guy or another champion.