The Dinobots. Oldschool cool. It was a little disappointing that Sludge (Brontosaurus, yes I know they've been discredited as a real dinosaur) was not in the new movie, but it was awesome to see Grimlock, Strafe, Slug, and Spike.
TF4 Optimus prime fan art by GoddessMechanic on DeviantArt
Optimus Prime from Bayverse Transformers - tumblr edit