weirdly enough, most adc rely a good deal on their spells to deal damages, so very few don't benefit from navori. IE additively increase your critical strike damage by 35%, making the bonus damage on crit a +110% (so a 2.1 damage multiplier). navori increase spell damage based on crit chances up to +20%, this is separate and will stack multiplicatively with crit on spells that, well... can crit. so multiplying together the 1.2 from navori and 1.75 from crit, you reach exactly 2.1, just like IE bonus. so the decision process is: -IE is preferable on champions that don't rely on spell damage. otherwise you lose on plain unmodified basic attack damage. -navori is preferable on champions that deal damages with spells (including passives, like kaisa). because they don't benefit as much from IE anyways. -in the specific case of champions that rely on modified basic attack that can crit (like draven Q), navori would only increase the bonus damage from it (not increasing the base damage of your basic attack), making IE much better. -in the special case of champions who rely on spells that scale with critical strike chances, but don't crit themselves (like xayah E, sivir Q, tristana E, lucian R), the benefit from navori is enormous since those spells will scale both from their crit ratio and the navori passive multiplicatively. though it may still be ambiguous, for example, tristana burst with her E, but dps with basic attacks using the attack speed steroid on her Q, you should pick navori or IE based on what you'll do more during the game. -in the case of champions who mainly use spells that can crit (like samira Q and R, garen E, etc), IE or navori deal the exact same damage. were the difference show is that IE deal more damage on unmodified basic attacks, and navori also increase the damage of spells that don't crit (for example navori on garen increase his Q and R damage too), but navori will often be favorable because it has that passive which reduce your spells cooldown when you basic attack. if you want, i can just give you a full rundown of how both IE and navori interact with a given champion's kit.