You are thinking of tit for tat, right? I remember reading about generous T4T where in ~10% of the cases they were generous [CITATION NEEDED] it performed better that pure retaliation. Now there is a new paper in Nature[1] that I just stumbled onto in trying to answer your question. It seems like extortion is at least competitive with a generous strategy, though I need to give it a closer read.

[1] http://www.nature.com/ncomms/2016/160412/ncomms11125/full/nc...