My favorite is probably Skeleton Surprise. There's just something super satisfying about *step, smash, step, smash* on repeat with a mace, almost like a dance. It doesn't really pose much threat by the point it tends to pop up and yet it's not as annoying as some of the others i could say the same for.

I have been taking my time checking out the new content so I haven't gotten to the mistlands related raids yet but with that part said my most hated so far tend to be "ground is shaking", "you are being hunted", and "you stirred the cauldron" for somewhat related reasons actually. Those ones tend to defy the norms of base defense. "You are being hunted" is obvious how, it's the only one you don't actually have to be at a base to defend and it can obliterate you easily if caught off guard. "Ground is shaking" is the trolls with their ridiculous reach that can bash your brains in through your earthen walls or from your trench/moat so they are one that basically requires interception or making sure they can't spawn to begin with. Then you got the bats in "Stirred the cauldron", it's not specifically that they are fliers or the drake event would be in this list to, it's that they are small spammy fliers that can get into the absolute worst of places like flying down your chimney and ending up in your kitchen or finding their way into your breeding pens. They are not a massive threat, but they are like a small horde of mischievous little gremlins descends upon your base to wreak mild annoyance, and they are super effective at that one.