I don’t like seasonal events that award pets. I understand why that’s a reward, of course; lots of people like having pets, some games have optional content using your little mini-pets for something else, and it’s an obvious vanity reward. But I don’t really consider “have another thing follow you around like the dozens of other options you already have” to be much of a reward. For that matter, I’m also not fond of seasonal outfits that either can’t be worn out of that event (looking at you, World of Warcraft) or are so thematically linked to that event that it looks weird at any other time.
This is not universal, of course. For some people, the whole appeal of a Christmas event is getting to dress your character up like Santa Claus year-round regardless of how inappropriate it is. And some people just want housing decorations for their abodes in EverQuest II or free mounts or whatever. So what’s your ideal event reward for seasonal content? What do you want to be given when you take part in these limited-time flashes of content?