Warrior Cats: Power of Three/YMMV

Base Breaker: Ashfur after Long Shadows. Was what he did reasonable or not? Probably not a good idea to ask.
Draco in Leather Pants: While no one has been able to agree whether Ashfur's actions were justifiable or not, he certainly isn't the innocent angel that many fans paint him as.
Ensemble Darkhorse: Purdy, Icecloud, Flametail and Fallen Leaves.
It Was His Sled: Hollyleaf dies (Not really). And she isn't the third either.
Magnificent Bastard: Sol.
Ron the Death Eater: Many fans consider Squirrelflight to be a selfish bitch for the sole reason that she dumped Ashfur.
Seasonal Rot: Generally considered to be the worst of the arcs.
The Woobie: All three heroes.