I use classic because I play on a fight stick and it just makes sense to me. Modern is hard for me to wrap my head around. I'm sure it sounds funny to people who find classic difficult but modern is less intuitive for me.
I enjoy the process of practicing execution and learning new set play and combos. The matches are tense but the training room is zen. Learning a combo or setup feels much like learning a new song on guitar, and when you finally get it, it feels great!
I also play Kimberly and personally I worry that modern is a large handicap for her. I use the buttons she is missing on modern very frequently. Without her install, she already has low damage and it hurts to have much of that cut by an additional 20%.
Even though I don't use it, I'm glad so many people like Modern. It's awesome that the genre has more players now. I think those that get upset about getting beaten by modern are forgetting that the other player is beating them in neutral and on timings as well. They aren't being carried by the controls like some would like to believe.