I can safely say that Darius is the safest pick out of all your choices (my bias is strong though). Tahm Kench I see banned a lot, so you probably won't get to practice with him enough to be good quite yet. Illaoi is a close second, she hits hard enough to wipe out entire teams if played right on top of pretty damn good range for a melee character, but the lack of cc makes it a bit tougher to pull her off if you happen to be behind. Ekko has a really high skill cap, but if you can make him work, more power to ya. Aatrox... don't. Just don't. In his current condition he's not worth it. His early game is decent, but if he doesn't snowball he becomes useless no matter how you build him.