Lightning
I also really disliked Yellowfang's Secret, but everyone beat me to it on the reasoning!
However, my least favorite Super Edition is Bramblestar's Storm. Maybe if I reread it, I'll like it more, but it really quashed my interest in Warriors as a whole for months because of how disappointing it was to me. Brambleclaw was, until that point, my all-time favorite Warriors character. I was happy with the kind of character he became by the end of the series. I was glad for his development by The Last Hope, and he really earned his spot as leader.
But he has not one, but two wacky relationship developments in that book. The first comes with Jessy, who is otherwise a pretty okay character, and I have no ill will towards her, just the really forced nature of her “i could love you” relationship with Bramblestar, which is kinda weird. The other thing is that he apparently has to get back with Squirrelflight? for some reason? like because they're the parents of Lion/Holly/Jay, they have to be in a relationship. They can't just be separated and on good terms. it actually happens sometimes, ya know? it just bugs me that they felt they needed to hammer in their rekindling romance after all their time apart and coming to terms with everything.
…i just basically disliked Bramblestar's Storm because i didn't want to read a love triangle and that's what about 50% of the book seemed to dwell on.
Yeah, I agree with that one… It was kinda boring to read about Bramblestar's dwelling feelings for Squirrelflight and the apparently new feelings he (could have) had for Jessy. Jessy herself was a good character, and I think she had so much potential, but it really felt like she was added for the sake of forcing Bramblestar back with Squirrelflight, and that's just a really bad way of looking at it. I mean, she, Minty, and Stormcloud were pretty decent characters, and I like how Stormcloud chose to stay in ThunderClan instead of going home (I think I might like him later down the road, once we see more of him), and I was hoping Jessy would do the same…but damn, not everything's about romance and sometimes two people just aren't meant to be together, even if they've had kids.
People moving on from past relationships but staying friends for the sake of the children happens a lot in real life (happened to my mother and father), so I'm not sure why it wouldn't have been okay to include it in Bramblestar's Storm and have a fresh start with a new mate, or not even one at all. He might have history with Squirrelflight, but there was also a lot of bad history which included her lying to him…which is all swept under the carpet for the sake of “family”.