Characters in British comics weren't usually called superheroes, although there was Marvel Man in the American format. I suppose that Dan Dare qualifies as a superhero. I was also fond of Jason Hyde, who could read minds and had fantastic adventures. Garth, in a daily strip, had super strength. British comics were mostly divided into those for boys and those for girls. When I got to read girls' comics, my favourite character was Lucky's Living Doll, a doll that came to life and could help her owner and talk to animals. I later followed the Modesty Blaise adventures in a daily strip.
I started getting American comics in 1961, although they could be several months old while displayed in British shops.
I have a soft spot for the Barry Allen Flash as it was the first American comic I ever got. He faced the Mirror Master in #119. I still love the artwork when I see it on the Web. My brother got a Batman comic at the same time. It was actually a year older than mine.
I later got Giant Superman Annual #1 although it had been published earlier than my Flash. I remember my brother teasing me when when he caught me pretending to be Supergirl. I had forgotten about that. I hope he has.
I then became enamoured of The Jaguar, an Archie Comics superhero. I looked his comics up on the Web and I can see why. Before he gains superpowers, he risks his life to save a Jaguar. When he gains his powers, he is attacked by jaguars (ungrateful &%^*s) and thinks to himself "the poor things are trying to bite me". Quite sweet and gentle as superheroes go. Tarzan would probably have killed them all (yeah, I know you don't get jaguars in Africa).
Later, my favourite American comic was Mystery in Space in which Adam Strange and Alanna shared adventures. At different times I became fond of the Legion of Superheroes (I really liked Saturn Girl), Metamorpho, Metal Men, Spider Man and the X-Men.
I read comics over and over again so I came to recognise my favourite artists. They would still have to be Carmine Infantino and Steve Ditko.
My favourite American superhero has to be Doctor Strange, though. I started my collection of occult books with the intention of creating my own Sanctum Sanctorum.
