How do you speed tune E2 Acheron with Sunday?

Kinda confused to wether stay with my slow Acheron (with ATK boots) or go for 135/136 SPD Acheron since my Sunday's SPD is at 134.

Right now I only have E0S1 Acheron but I'm planning to pull her E2.

Also random question: Out of these 4 (Sunday, Sparkle, Robin, Tribbie) which one is the best for her?