Best thing was...

The villain. Not that Dave had a great story or a great plan, but just how they animated him was incredible. It's pretty clear the filmmakers were fans of the 'Octodad'game, since the Dr Brine persona was basically a huge homage to it.

But yes, the animation for how Dave moved while in his human disguises was fantastic. Not even that, it was also immensely creepy to watch at times. As I said, Dave isn't incredibly written, even his name isn't that scary / humorous (if it's meant to be a joke on how un-scary it is), but the animation alone made him the best element in the film. I love his introduction especially, how he walks in on the ceiling, then falls and lands in a slippery heap, and then slowly unwinds and untwists himself back into a vaugely human shape