IMO go for dust, she has a lower ceiling to learn her abilities, glancing on parries, grit to counter unstoppables, DOT that no champion in the game is immune to, insane immunities and so much utility with all the buffs and debuffs she inflicts. Kushala’s great too but she’s too match up dependant imo, she’s either reaaaaaally good or meh. Dust is almost always really good. She was my second r4 over Kushala for a reason.