I rather like the response from Geese, it’s really as simple as that. Play through all the characters until you find one that “clicks” or that you have more fun playing as. It’s really as simple as that.
I did the same, myself. I was playing Sakura, then ended up maining Rose in Street Fighter IV. When Super came around, I started playing Guy, just to try him out. But after I started playing him, I couldn’t stop. I couldn’t pick anyone else but Guy and I kept playing with him until I got decent. I’m not super pro or anything, but I can at least make a little trouble with him while I get better. Now, just because you have fun with a character, doesn’t mean that you’re just going to start winning, by the way. I’ve come to realize that losses come with learning a character, however many it takes for you to learn the ins and outs of said character. You have to learn your ranges, what you can and can’t do against certain opponents, what your fastest move is, what your longest moves are, and the properties (invincibility frames and what-have-you) of all said moves.
Once you find a character that’s fun for you, you have to “tune in” to that character and learn everything about them, not just how to do their special moves. But it doesn’t really stop there, either. Once you learn what your character can do, you’ll have to learn what other characters can do so you can better fight them. So once you find that “one” character, you’ll be good, so play em all.