Let's start with the best.
I'd argue Astro Boy over Devilman but generally, yeah, both are pretty big. Kami-sama Tezuka wins over Kooky Uncle Go in my book, but only by the fact his methods have been the standard for 50 years (ie: working so much you don't sleep and die)
Devilman's influence is partially quite apparent in really dark and more brutal works like Berserk, Evangelion, Parasyte, Bastard, CLAMP, and game directors like suda51 or the creator of dark souls, but it also influenced the medium in more subtle ways.
It paved the way for shonen manga to display more brutal and violent content and scenes with meaning behind them. It popularized bishounen gay themes, sexuality and christian/demonic themes within shounen manga too.
The anime of Devilman was also one of the first prime time anime which at the time was thought of as not successful.
Set the standard for shounenshit and then everything that came after it failed to live up to it. Imitated and parodied to no end in the 80s and 90s, less so today but it's influence is still felt.
Mitsuteru Yokoyama deserves to be as wildy known as these two (I suspect he probably is in Japan but I don't know). Shotaro Ishinomori is probably more known than Yokoyama but I think Yokoyama did more important things in manga all things considered.