I actually feel, given the roles of the Samayasattva and the Jñanasattva in tantric practices, that whilst Yeshe Tsogyal is most often used as the most suitable form of Samayasattva, when you look at what attributes are most suitable for the Jñanasattva, it is obviously Guru Rinpoche. Thus the predominance of GR as Guru.
But there are probably exceptions; the Choling Tersar Green Tara comes to mind... probably others too.
"When a Dzogchen Yogi hears Shakyamuni Buddha turning the Wheel of the Dharma of the Four Noble Truths he hears Samathabhadra proclaiming the most profound Dzogpachenpo." - Nyoshul Khen Rinpoche