>>73521637
The answer is always Sisters of Battle.
I have Dark Angels, a small thing of Tau, and just started Custodes. I played DA with a sprinkle of Sisters since 3rd, off and on for 5 years, and won maybe 3 times. I hated it, and it made me leave the game. I'm a terrible loser and it wasn't fun going and losing to people week after week.
Fast forward to 8th, I get in on the new stuff, and add more to my sisters. I still lose, but now it's not as bad. In fact, I just love getting to play them. It's much more fun because they're adaptable. I don't feel completely screwed if I don't have enough exorcists or penitents. If anything they make great distractions. Your opponent will hate you for the miracle dice, but they're so much fun.