A few random pics:
Spiderman: he's essentially a nice, fuzzy guy who's being put through some horrible tests of life. He's matured a lot over the years, without ever losing what makes him Peter Parker, the timid science nerd. He can be both a hero and a bit of a coward (sometimes). He's often inventive and decisive, but sometimes he just doesn't know what to do. He can be cheerful, but he can do the brooding SOB-thing just as well as any of the so called "dark" characters. He's simply more diverse, more ambiguous and, to me, more interesting than characters like Batman. The learning curve is much steeper (and more complex) for good people that have bad shit happen to them than for people that already love to sit in the dark and be "badass" all the time, imo.
(And people really need to stop using the relatability argument, imo. I'm sure it works for some, but it's not what makes Spidey a great character.)
Iron-Man: when generally unsympathetic, overly capitalist pigs decide to do "what's right", interesting stuff will happen. Period. Also, Iron Man just looks cool.
Spawn: He's got the looks, the character, the powers and the stories. Well, most of the time. And he does the brooding SOB-thing much, much better than Batman!
Hulk: Born from a simple (but intriguing) concept, gradually developed into something unique. He's also the only character in Marvel who can actually get away with drastic changes in personality and behaviour all the time, imo. In fact, they make perfect sense. The biggest downside is that most writers aren't interested in realizing Hulk's full potential as an object of the mind. They just make him smash and say stupid things. I guess that's one way to look at it.... 😕