I vote aye for the leader of the clan, or a man whom the clan leader chooses from his clan. That brings two questions. There is only one representative for each clan, and is it agnatic((males only))?
There are a couple of conflicts with the questions that you have proposed. The first question's (the one representative) conflict is Clan Yotoli, who has two heads of the clan, one male and one female. The Yotoli, however, sees these two as one person. If one of the heads die, the other is ritually sacrificed as they believe half of a person cannot rule. Overall, the Yotoli's leaders, after close examination, should be fine on the necentlaliliztli ((assembly)) as they are treated as one by their clan.
and is it agnatic((males only))?
((I was the first one to step up, but it was quite hidden in my post. I'll make a clearer statement soon.))Seeing as no one else besides the Maximotl and the Coaxoch had stepped up yet to announce their desire to take the trials of becoming Tlatoani ((Head Speaker)), Ceccuetlachtli, after much thought, stood up from where he was. Although not as buff Julius, Ceccuetlachtli still had an athletic build. "I, Ceccuetlachtli of Clan Cecuecacayotin seek the position of Tlatoani and shall undertake the necessary to become one."
The Ixtozoa is not about simple endurance. It is not just about lasting longer than your opponent. TO be a good Tlatoani, something more is needed. True, one should endeavor to stand as long as possible, but how you stand is also important. Would a good Tlatoani huddle on the ground, or brace himself in the face of the wind? One might afford him greater endurance, but at what consequence? If an achcuahtli stands in place in the night's chill without flinching, and maintaining the proper bearing of a leader, especially if (s)he outlasts all other contenders, than the Tlanextic will have no trouble voting for the next Tlatoani.