//OHHHHHHHH this is HARD.

If it came down to it, I would have to choose Series Four.  

I love Series Three Master for his expansive, terrifyingly determined ambition, his brilliance, his capacity to subconsciously manipulate an entire planet via a cellular phone network, to establish an entire plausible false persona, to learn enough about an earth-based socio-political system to ascend to its highest ranks, to design and build a literal floating island fortress as well as an armory of black hole converters, travel to the end of the universe and recruit the humans there to his cause, etc etc etc.  He is never more whimsically sadistic than in this series, and he gets arguably the furthest of ALL faces of the Master in actually defeating the Doctor and establishing lasting dominion over his favorite planet.  Series Three Master is a truly impressive “anti-Doctor.”  

BUT.

Series Four Master is a broken, rock-bottom, frightened, tantruming child, and as pathetic as he is, he is my favorite for that very vulnerability.  All of my favorite Thoschei shipper moments come out of the End of Time episodes, and I believe End of Time was a turning point for the character, planting the seed that would become the reformed Master in Missy (I argue, in fact, that without Moffat at the helm, that reform would have come sooner still, but that’s for another meta).  Series Four Master cries. Series Four Master laughs like an idiot. Series Four Master pouts when the Doctor calls Donna his “best friend.”  Series Four Master throws his hands up in jubilation when the Doctor confirms that the Drums are “real.” And in that moment, Series Four Master reminds me of myself when someone I love believes how much a chronic illness is tormenting me.  

Series Three Master is the Master that hooked and impressed me, but the “king of the wasteland” is the Master that convinced me he was capable of being loved and forgiven.  

Also, John Simm looks … peculiarly sexy with bleached blond hair, scruff, and eyeliner.