Which pack do you most regret buying?

For me, it's most certainly Outdoor Retreat. It's not that I hate the pack, but it's the one that I use the least. I sent my Sims to the vacation world a couple of times over the course of a few weeks after the pack was released and then... nothing. I never used any of the main features ever again, only a handful of the clothing and the B/B Mode objects. I've never even fully explored the Herbalism Skill. I don't regret buying it per se, since I like some of the clothes and collectibles, but if I could go back in time, I would wait for a sale for sure.

And I still don't own Eco Lifestyle, so I can't comment on this one.