Both are simply wonderful. The fairy-tale quality of Star Wars (essentially just fantasy in a futuristic setting) takes your breath away, but the originality of Warhammer blows my mind! When I heard the Force Commander say: "I command in the name of the Emperor," I was absolutely thrilled! For once, they moved away from those clichés with federations and atheism/free religion and created something truly original!
By the way, some Space Marine phrases carry a lot of meaning — "Heresy grows from idleness" (needs no comment) or my personal favorite, "It is better to die for the Emperor than to live for yourself" (if you understand the word "Emperor" here as some kind of idea, then this is the creed of many, many people). And the Tech-Priests awakening the machine spirits... And the Eldar with their rustling, lifeless voices... And the spore-reproducing Orks with their fantastic illiteracy... Not to mention Chaos, which I sometimes played as just to hear what the troops say... Wow!:)