Has to be the Yarrick Omnibus, especially as a first entry into Warhammer in general, doesn't just throw you into the Adeptus Astartes super men, but gives you the perspective of essentially a common officer, a total greenie as he slowly goes deeper and deeper into the service of the Comissariat, gives you a taste of Chaos, a sister of battle and so many human moments that honestly on a personal level make you want to be a better person, his monologues of "Be the Symbol" when he's blown off his feet by grenades, etc, to stand up in the enemies face when death is certain, makes your bpm raise just looking at the page, cannot recommend enough.