As of NSC 2.11 the balance is generally considered good enough that you can play whoever. Ray and Kudlak are generally agreed to be the best, and Cait & Sith are generally agreed to be the worst but anyone can win.
Tenryo's 2.11 tier list (characters not ordered within tiers):
S: Ray, Kudlak-Sin
A+: Cerberus, Rui, Celia II Kai, Catherine, Cthylla
A-: Kagari, Hikaru, MG Hikaru, Celia, Bravo, Lupinus, Vein, Hermes, Cait & Sith
This is a matchup chart/tier list made by Tenryo for Chaos Code version 1.02, and doesn't include Kudlak-SIN due to him being console exclusive. The following is the closest thing you'll get to anything accurate, and it has been approved by many players. Always keep in mind that tiers aren't an absolute in a match and are in most cases exaggerated. Feel free to disagree at anytime.
Tenryo's Chaos Code 1.02 Ranking:
S - Cerberus, Rui, Celia II Kai
A - Cthylla, Catherine, Kagari, MG Hikaru, Hikaru
B - Vein, Bravo, Celia, Hermes, Cait & Sith