Sisters of Battle
Guardsmen are SUPPOSED to be the whole "normal humans fighting against unknowable evil" thing, but they have kind of fucked that up over the years by giving the Guard some of the biggest and best guns around. I still remember when the Leafblower guard list was going around and thinking "and these guys are supposed to be the underdogs?"
Sisters have a better schtick on top of that, being martyrs who will willingly sacrifice themselves for others, a bit like the Lamenters actually.>least favorite
The "secret incorruptible warriors" worked better when they were a minor faction with barely any fluff, and furthermore were folded into Daemonhunters alongside the Inquisition.
Now however, with the expansion of the fluff the GKs are turning up all over the place, and you simply can't mindwipe everyone to keep it a secret.
Furthermore they feel like the 6-bladed-razor of factions, we already had Space Marines, who were THE BEST OF THE BEST with ATSKNF, 1000 initiates dying for each successful marine, having very few numbers but still kicking ass, and GKs bring literally nothing new to the table besides trying to turn those traits up to 11. Again, GKs worked as part of Daemonhunters because they were just one small part of a much larger organization.