Which expansion pack is the most worth getting

I agree with @PugLove888 and @suzushka . The Club system from the Get Together EP is awesome! It keeps all club members in the same general area and actively engaged and socializing with each other (NPCs included) rather than all just wandering off and doing their own thing, or even leaving the lot entirely. Here are some uses for Get Together clubs:

1) If your Sim is dating an NPC you can create a "Date Night" club to hang out with your boyfriend/girlfriend without having to worry about the timer or completing goaled tasks that come with a formal "date" event. Have a fun, relaxed night of dancing, watching a movie, go to a museum, whatever you want, just enjoy each other's company.

2) If your Sim has moved out of their family home to attend Uni, or for any other reason, you can create a "Family Fun" club so you can hang out with your (now NPC) family members-- have fun at the park, go bowling, attend a festival in San Myshuno, whatever you want. It's also great for keeping them all in the same place for holiday get-togethers. Btw- you can also use the "Always Welcome" perk if you want to do a sleep-over at your old family home, or raid their refrigerator for a free meal! ;-D

3) If your Sim is at Uni and has lots of Uni NPC friends you can create a Sorority or Fraternity club or any other type of mixed Uni friends club. It's a great way to keep them all together for a night of partying or a fun day at an arcade. You can even use it to send them all to a place like Sulani for a day (or more!) for a sort of mini-Spring Break. Did someone say Beach Party?

These are just a few of the ones I use. There are many, many other ways to use the Club system from Get Together, kid's clubs, teen clubs, heck when the new Nifty Knitting pack comes out you could even have a knitting club!