Used to main
top last season. With 200+ games I'd say her skill cap is one of the highest in the game and would be the most rewarding out of those 3.
With her parry(to counter any type of stun or burst), low cooldown dash(to catch mobility), auto attack reset/guaranteed crit(for burst against Squishies) and true hp% damage(for tanks) she has the tools to effectively win against any champ in the game if you're able to outplay them.
Her only weakness is that she has no business participating in team fights since there's too much cc and damage getting thrown around to survive
Irelia used to be good but her stats were gutted and she's statistically one of the weakest champs in the game. She's fun but not as effective as the other two.
Camille is a weaker, sturdier version of fiora that's much better at banking and team fights.