So far a little, but fruitful experience with Adsterra. What's good about Adsterra is its developed advertising inventory + sane quality of traffic. Their social bar (essentially similar to the usual in-page push) is good because it has a quality built-in creo builder + a detailed preview of the resulting creative (for example, a png will have a black background, it's visible). That's something a lot of grids should learn. Popander - well, the ratio seems nice, but I'm not an expert on it, so I will not say much about this format.