My vote goes to Sammy & the Black Knights, I've felt firsthand how much destruction they can cause.
That said, you should probably wait to get your paws on the new Blood Angels codex (I think it is out next weekend?) before making a final decision.
And the new Blood Angels Marine box looks soooooooo good...
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons