I can only tell you which ones have made the biggest difference for me. FYI, my style of play is storytelling and screenshots. I like all the expansions I have, but my favorite two that have made a huge difference in my enjoyment of the game are:
City Living -- because I love highrise apartment living (the views, decorating the apartments, the "vibe" of a city apartment).
Get Together -- because being able to form groups/clubs opens up a lot of new possibilities for gameplay.