What kind of gameplay do you like? Are you a family player, supernatural, career oriented? Different packs will be better for different simmers.
One pack I will say is an absolute must buy regardless of playstyle is Parenthood. It completely overhauls child raising and actually makes playing with kids matter in the game. Combined with the scouting that came with seasons, it actually made children in this game have something to do.
Expansion pack wise Get Together and City Living are both great packs that add a lot of great CAS and BB as well as features. Get together comes with the prettiest world in the game and city living has festivals that are really fun and great for meeting new sims.
Otherwise it's personal preference, Vampires is one of my favorite packs but it won't be a good value if you don't play supernaturals while Toddler stuff would be great for someone who plays toddlers a lot but not valuable for some usually skips that life state.
