Both are fine, and different cigars will prefer a tad wetter or a tad dryer, but both 65% and 70% are good for about 90% of the cigars out there. Hence, they are pretty much the two most common standards.
That said, I have 70% beads in my humi. I figured that I could just dry box for a day or so those cigars that smoke better when they are a little dryer. As it turns out, I don't quite have enough beads for the size of my humi anyway so the 70% beads only keep it in the 62-65% range and most of my cigars seem to like that range just fine. I'll probably eventually replace them with 65% beads (and enough for my humi's size).