Which expansion pack is your bet? I'd choose Generations. I think that Generations is the best yet. It expands your family options in the sense that family life is more fun, it has a lot more interactions between family members and it makes your Sims seems more alive than previous expansions, it also adds a lot of stuff for the kids to do, new clothes, costumes, proms, dating, giving flowers, pulling pranks. Lastly, without that there a lot you could do with kids and teens accept grow up.
I would either say Generations or Late night. To be honest, most of the later ones such as Pets and University lag my game so much that it almost is unplayable now-a-days. Late Night added so many things that my young adult sims can do in the city, especially the ones that lived in the city for their job. I'm particularly fond of how they increased the amount of instruments your sim can play. Generations like you said is also a very solid expansion. It just made my sims more realistic in what they do, but I don't like the popup that comes up every so many minutes saying, "UH OH YOUR SIM GOT TRAPPED IN THE ELEVATOR AGAIN, SHARE IT ON FACEBOOK". The one that made lofts better was also pretty good in my book.
