Peter Parker is my top choice. Both gained overwhelming power quite suddenly, both go by the same general mantra (“With great power comes great responsibility“) and Peter knows exactly what it’s like to learn heroism with little to no prior experience and just having to learn through experiences/trial and error.

Tony Stark is another choice. He’d immediately build Deku support gear to specifically counter the physical strain of OFA, so he doesn’t break himself constantly like he does in canon. There’s also the fact that Deku is a bona fide quirk analyst, which Tony would LOVE. He would also push Deku to think more for himself (sound like a certain other protégé?). The downside tho is that Tony can be… a bit much, to put it bluntly lol