Angron and his lot are knuckle draggers. I prefer the Alpha Legion. Subterfuge and infiltration are awesome! It's also a nice change from seeing both traitors and loyalists alike beat their chest and run into battle guns blazing.
Red Corsairs are a Warband not a Legion (technically a renegade chapter but their size probably qualifies them more for the role of Warband these days).
Blood Gorgons but they are not a legion, but they hay honor and respect for their brothers unlike the rest legions who can't work on the same page for very long because they care nothing but themselves. The chaos legions will never win because they can't even get their Primarch's out to fight because off daddy issues.
Erhm. Word bearers. From the Daemon World of Sicarus, Lorgar watches over his Legion and orchestrates the vast corruption from within that the Imperium suffers at the hands of his cults and covens. Unlike many of the other Traitor Legions, the Word Bearers have remained a unified, if loosely organised, military force, the main ruling body of which is known as the Dark Council, which rules in Lorgar's absence.