Classics:
Definitely Cyclonus. While his alt mode may be a bit iffy at the rear, his robot mode more than makes up for it. I love messing about with this guy and although his arms are a little limited in motion, he can get into some really imposing poses. I think the darker colour scheme also helps with this.

Henkei:
My favorite would definitely have to be Megatron. I love the colours, it has good use of the chrome and the transformation is just the right level of complexity for me.