Insanely difficult and wide ranging question. I don't really like having absolute favourites, but if you're asking me for a Really Good One, the twin Tekkaman designs from the infamous Tekkaman Twin Blood short are like... truly holy to me, although that has more to do with how they're portrayed in motion than the designs in isolation. That's just one for you, I have 10000s that live in my brain in a endless line of canonized saints.