Not sure if the Booper Collab counts, but the Kosmo's are awesome. Futuristic to some end, combining with a skull which everyone seems to be okay with. Then to turn around and have the Gemini and Apollo GID in green or blue. There are just SO many combinations and themes. I like blue so the Apollo is my favorite, but $300+ aftermarket is too much for a cap. lol.
So yeah, that's my favorite cap and colorway.
But the KK FR is probably my favorite run/series.