Play Ryu to understand how the game works, including how to control your character, execution (specials, combos, ect), spacing, zoning, all that good stuff, then switch to whoever you think is interesting. The most important thing is to pick a character that matches your play style. For example, I don't like Chun-Li, but I'm all about low-execution, footsie-oriented characters, so that's why she's my main.