A ball!

You pick up your harness and put it over her head. Kiera is confused as to why she´s got these straps running around and over her head but doesn´t question you. After buckling it on nicely you pick up the three balls you have and order Kiera to open her mouth.
The first ball is yellow and easily fits into Kieras mouth, but it doesn´t really muffle her speech that much.
The second ball is black and fits okay in Kieras mouth and muffles her speech more, along with making her drool.
The third ball is red and can barely fit into Kieras little mouth. It´s highly uncomfortable for her and muffles any protests she might have but she doesn´t drool as much.

Which of the balls do you pick for her?