Which heroes are the most popular/admired by the public in-universe?
The Fantastic 4 (all of them, maybe not Thing due to his monstrous appearance?)
Thor apparently is worshipped in a lot of planets across the whole universe, i'd say he is a contender for most famed in universe at Marvel. But at the same time, the Avengers as a whole are just as widely known as a threat by most Galactic empires by now...
At Dc it s pretty hard to contend with Superman in a matter of fame, but perhaps Wonder Woman has had better press releases at times; i concur though that the green lantern are more likely known in the wider cosmos, if not by name at least as a role...