Sokaku Takeda, then Morihei Ueshiba, then Gozo Shioda, Koichi Tohei, Terry Dobson, Don Dreager and time allowing
Kisshomaru Ueshiba, Hikitsuchi, Osawa (Sr), Nishio, Yasuo Kobayashi (when he was younger) and a whole host of others too numerous to list.
And while it would be interesting to see my own sensei or senseis that I know well when they were younger, I think I would use time travel first to see those that I have missed the opportunity to know.
But, be prepared, as often the myth is more impressive than the person which is why I probably would not select Musashi, as I think I am content with his story as it is.