That's an interesting question, because it is plainly made clear to readers that Cherry likes whatever Dally has got going on a whole lot.
She looked at me quickly. "I could fall in love with Dallas Winston," she said. "I hope I never see him again, or I will."
That's an amazing statement from a girl that is fairly committed to nonviolence and hates criminal behavior. In fact, she even detests it when her boyfriend drinks alcohol, yet she admits that she is deeply attracted to a guy like Dally. Dally is a legitimate criminal. He's such a "bad boy" criminal, that Ponyboy lets readers know early on in the book that he doesn't like Dally.
[...] he got drunk, he rode in rodeos, lied, cheated, stole, rolled drunks, jumped small kids—he did everything. I didn't like him, but I had to respect him.
Readers might argue that Pony's opinion of Dally changes throughout the story, but I don't think so. I think Ponyboy respects Dally and trusts him, but I don't think Ponyboy would ever desire to be close friends with Dally. On the other hand, Cherry knows that she is so attracted to him that she needs to stay away from him. Bob is essentially the same person as Dally except on the Soc side of the equation, and that is probably why Cherry is his girlfriend. If you could ask Cherry what it is about those boys that she likes so much, she couldn't tell you. She tries to explain it, but everything she says is so vague.
"I know I'm too young to be in love and all that, but Bob was something special. He wasn't just any boy. He had something that made people follow him, something that marked him different, maybe a little better, than the crowd. Do you know what I mean?"
Cherry is exceptionally good at reading people. That was made clear to readers early in the book when she figured out that something bad had happened to Johnny. She simply knew. That is what she tries to explain. She knows that there is a quality about guys like Dally and Bob that instantly causes other people to gravitate toward them and respect their actions, words, and person. She sees in those boys the capability of strong, male leadership, and I think that is what she is ultimately attracted to.