This is a very interesting thread, thanks for the useful links.
Some masternodes seem to be both very cheap to run and according to these indexing websites also offer extremely high profitability; I'm assuming these statistics are subject to very rapid change, however, and the longevity of many of these projects are also in question.
Therefore, what would be the top 3 most profitable and cost efficient master node coins you would recommend at the moment ?
Dash is going to be great with upcoming version. Axe is still very cheap and easy to mine. Pivx dev left the project so its unlikely theres going to be anything new besides light updates (and how long they would last). the rest has empty or no source code available. there were couple more i think but they didn't survive this summer i guess