I went with Farm Life because it would probably give me the most gameplay.
Open Schools would have been nice with Sims 3 because then I could swap to my other sims without loading and such. I don't want to watch my sim kids raising their hand, falling asleep, doing misc projects, etc while my adult sims are doing nothing productive at home.
No interest in the rest except for the alien world and maybe the carnival
The carnival would be nice if done right with many games and many rides, psychic career, magic career, acrobatics, fire eating, knife throwing, contortion, clowns all things sims could master and join the circus doing. etc. I would literally want a destination world that was nothing but the carnival maybe with some rentals. I want my sims to sit in a tent and watch a show, get on the rides, actually play the games. No rabbit holes.
As for the alien world, Sixam is beautiful but it was messed up to work so hard to get there and there was absolutely NOTHING to do but take some pretty screenshots..lol I wouldn't mind the world getting fleshed out with alien type activities. I would want the aliens to be more aggressive with their behavior towards regular sims. I would love for them to think the human sims are beneath them. If an alien marries a human, other aliens would shun them and disown any children from the marriage. I still don't think it would be enough to warrant an expansion pack.