What are some of your favorite renegade chapters/warbands?

These are technically, still loyal chapters (to the Emperor, if not the Imperium) and fight xenos, chaos, and the corrupt Imperium whenever?

Soul Drinkers come to mind.
Sons of Malice come to mind.

Soul Drinkers are my top choice because of how different their defection is and how everything played out. Most other renegades end up feeling more cliche evil and haven't really been fleshed out too much.

The few short stories about the Avenging Sons under Captain Gessart who went renegade had a bit of promise, but really haven't been expanded upon.

Yeah, renegades should be touched upon.
Going to keep tooting my own horn here, but the Sons of Malice have such a badass paint scheme, such a shame there's not more about them.

Crimson Corsairs would be an obvious addition. They are one of the most prominent renegade chapters and are arguably the most dangerous.

And while I know they aren't at all loyal to the Emperor, they are considered Renegade Chapter in terminology.

Do you mean Red corsairs?

But the Sons of Malice are traitors to the imperium too for they follow Malice/Malal the lesser chaos god that hates everyone, chaos and the imperium

; )

:| Khorne is best....

Would love some renegade chapter in the game, but chances are pretty slim i guess