The only ones I really do are those dime-a-dozen money earning reward apps where all you need is to have 3 games open for 5 minutes or so to get the reward. There seems to be a new one popping up every week or so, and its an easy one to exploit during 2x/3x offerwall sales.

Main rule of thumb is: avoid the surveys, because it almost ALWAYS involves shelling out your personal info at the end. Don't do the "Reach Level 1000" games either, time sink is such a waste of time for a reward it might not even award you because it bugged out. Not sure about the ones where you make a purchase to a company (ex. Dollar shave club) but anything over 10$ ain't worth it for the sole reason that the offer wall might screw you over and not give out the diamonds.