They are doing their homework for you. If they are featuring particular advertisements and you are aware that these sites are the very best sites in your niche and they have been around for some time, you understand at some level or other, their monetization version is working for them. Look closely at the monetization models utilized by competing sites in your specialty. If you realize that a whole lot of those used Adsense, then
then odds are, Adsense must be your first choice.
If you realize that a whole lot of those used CPA advertisements, then this could be the best way to go.
Irrespective of how they earn their money, look closely at their monetization version. In the minimum, this gives you a very clear idea about which monetization models to experiment with. This does not imply that you are likely to stick with this specific means of earning money but it’s definitely far better than rolling the dice and taking shots from the dark and hoping to get lucky.