Sanguinius. I mean, we've got the most hardcore primarch. he broke the back of a bloodthirster over his knee. Horus held sanguinius in higher regard than any of the other primarchs, and even himself. He's awesome incarnate.
plus, I love the models. Dante, Tycho, Mephiston; they are all awesome, and the armour reminds me of the works of Michelangelo and the like. I love that stuff. Now, I'm not the biggest fan of our codex, but our fluff makes up for everything. I like how they are portrayed as cursed heroes, no matter how great warriors or tacticians they are, they will still fall one day. either in combat or to their own flaws. It's refreshing. space marines heroes in general are boring and uninteresting to me; I'm not a fan of the whole "best of all time" thing. that they seem to give out like free candy these days. Calgar? yeah yeah, noone can apparently kill him, he wrestles avatars and orks for fun, whatever. no flaws. boring. Tigerius? tap the hivemind, whatever. best psyker there ever was. too perfect. boring. cato sicarius? apparently best h2h captain ever, which is bs anyway. boring. pedro kantor is the only one i find interesting, fluff wise. maybe khan, cause he chops heads off for a living.
Our dudes? Our chief librarian fell to the curse and overcame it. he still wrestles with it every single day. Corbulo? the dude doesn't even have a power weapon. not much to say as for Dante's flaws, but even Calgar sees Dante as a better commander. plus Dante looks like a piece of art. Tycho? well yeah, he got his face disfigured, and went crazy. our poster boy even fell to the curse and got himself killed fighting orks.
I love those imperfections. they make us unique. and we are vampires, whole love art, sleep in coffins, and maybe, just maybe, we might go nuts and drink blood. There's no other chapter who's got better fluff than us. none.