Okay more detail this time...
1) Spider-Man: he has a compelling backstory, and motivation, and cool powers, but the best thing about Spider-Man is his mind. When written well he's incredibly cleaver and resourceful, often outmaneuvering and out thinking character who are more powerful and more intelligent than he is.
2) Captain America (original) because he stands for the ideals that America reaches for, he's human despite it all.
3) Iron-Man: When written well he represents the promise of technology. He uses that technology in a direct and efficient way. Unlike some supergenius character. While not quite on the level of Peter Parker, when it comes to thinking on the fly, but he can use his IQ for something more than Brute force thinking, unlike certain other characters I could mention.
4) She Hulk: Come for the ****, stay for the humor. Yes she big and sexy, but she's also a fun character, on the same level with Spider-Man for humor and close for cleaver fighting.. This of course is when she's not being written as a doormat for Rulk to wipe his feet on.