I really like the style and color use here. There is a lot of personality in the shapes used and the construction of the characters, which is impressive considering they're just busts. The shading on them is very nice and consistent with light source (I especially like the glow coming from their eyes), however they appear to be shaded using different techniques, the purple one has a very apparent grainy texture, whereas the blue one is much smoother and even has some extra highlights on the hair that indicate a plastic or ceramic surface. Being that the two characters are together the texture difference is a bit jarring. I like the choice of background here, but I think it would be better suited if it were lightly rounded along the edges to better emulate an old tv set. I question whether or not the red outline is necessary, I think they have enough boldness to stand out without it, but its not really negatively effecting the drawing in my opinion. Also on the blue on those little stray hairs at the top would probably cast a light shadow onto her ear, so look out for those little things.
I hope this helps in some capacity, great work, keep it up!