I like Ordinatus Armageddon - bears the massive plasma-based Nova Cannon, capable of blasting apart enemy Titans with one shot or destroying a tank detachment with a single salvo. I think allmost all ordinatus is badass. Also Bjorn the fell handeds dreadnought armor.
Anything orky is awesome. See that Russ over there? Now it's mine. That Prism Tank? Mine as well. Oh you liked that predator? Well too bad, it's now red and covered in scrap metal.
