I guess not a big surprise to anybody, but some guy actually wrote a research paper for his Masters degree which collected a bunch of data from each case opening to compare the ROI's on each case. The sample sizes were about 2000+ cases each type. Perhaps not enough to give a perfectly accurate ROI, but I think it's pretty close. Long story short, average case opening will return you ~35% of the cost of case + key to open it. Best case to open is CSGO Weapon Case II, worst case is Gamma. More details here: R2Pleasent Gold | Why Opening CSGO Cases is a Terrible Investment As for Case opening sites, all I can say is lol. Those guys are probably giving out less than Steam by a wide margin.