The Old Republic.

I say Obi-Wan

Satele Shan was definitely the best Grand Master in all Jedi history

Grandmaster usually implies leading the Jedi council too, correct? Qui-Gon explicitly rejected the idea of being on the council. He likely found it to be too restrictive. It has to be Obi Wan, I believe he bridged the gap between traditional Jedi and free Jedi.

I think Eno Cordova was the only one that could out Qui-Gon Qui Gon, who notably didn't want to sit on the council, let alone lead it. I feel Cordova would have been more flexible and generous as a Grandmaster than even Obi-Wan.

That's fair, I think Eno would be a great choice as well