Times Silent Keeper
GlaDERP Security - All of them were pretty neat. I loved the cyber feel to them.
Arthurian Ram / Eagle series - I liked the contrast of colors, considering how they resembled the animal pretty well, that was a plus for me.
Lightshow series - Really, really impressive design.
Jameson series - The one that was initially released, the design for that was lovely.
Anchorman - Portrays the image pretty well IMO.
Headless Horse - Creepy, cool, and great in design.
And last but not least...
Derpmachine! - Colorful, but the entire design just seems to fit even with all the eyes.