They usually put out the good stuff on holidays.  Tourny's have much more diverse reward packages than they used to.  Depends on what kind of rewards you are looking for as well.

Brethren units, Dread Fleet, Idols, Etchings, Pearls, Gears?

I would have to agree it is nice when the tourny's stack on each other like  XP hunt, prize hunt, pvp, and a BH adventure all at the same time.  That can really maximize rewards too.  Don't ferget to punch out those personal missions too.

It depends on the points required to get a reward and the type of bh your in. For instance if you're in a bh that doesn't do much pvp a bh pvp tourny won't offer you great rewards if only a handful of people are involved. Like the last xp tourny required far too many points for little rewards, 7500 just to qualify. 

The tourny's with the best rewards generally are prize ransacks when they offer fleet and don't require more than a few hundred points for each level. Any tourny that offers mercs generally is a waste of effort. Something else to note is how long the tourny lasts, generally those that last 3 days or more do give out better rewards.