GSP, Silva and Jones have similar situations. Dominant to the point that most casual fans clamor for them to make super fights. More so, the Dana wants them as well, but only for monetary reasons with total disregard for the purity of the sport.
My personal belief is that GSP takes the most grief in this triangle. There isn't a smaller fighter in this equation for GSP. Silva is willing to fight GSP so he's a supposed true warrior, same goes for Jones willingness to fight Silva. Jones and Silva are similar in size and their fight makes the most sense if one of these fights needs to happen. NONE of them should happen.
I don't believe any of the three are the #1 challenger in the weight class above. Silva beats GSP, Jones beats Silva and Cain beats Jones. None of those results would or should have an effect on any sane P4P list. Instead of berating a man who chooses to stay in his division and take on all challengers, berate the man who wants to call out fighters with a clear size disadvantage.