I think most people usually prefer the red dragon gown. Killer set is good for those that want a lot of speed added too and not just attack. Unless you put really high spars it wont give as good atk as the atk set (RDG, bloody war boots, gold bracers, snow ears)

Nimbus spar can be inserted into the RDG no matter what you're alchemy is you just need to make sure you compound them in the right order ^^