I would probably agree that @luisfsk is the AI that gives me the most trouble. I usually have to draw once or twice before killing. I take 8 draws vs full immortals but that's just a matter of patience. Luisfsk's AI likes to dance around making me focus on aiming.
I'd be interested in collaborating with @marwinberna and @luisfsk on either helping tweak our respective builds or creating a new AI for arena. A super hybrid immortal that is impossible to kill in less than 2 draws but can kill anyone in less than two draws sounds like a worthwhile project.