Sorry, but I have to disagree.
I find the artwork for Astro Knights some of the best we've seen so far in Smash Up and the art for Changerbots couldn't be more fitting. Also 3 out of 4 factions are done by artists AEG has collaborated with in the past for Smash Up.
What's the one that hasn't?
Also I disagree that Astro Knights have the best art. Werewolves, wizards, aliens, to some extent the dragons have much better art.