First, buy your games at www.cdkeys.com . The bundles there are cheaper. Your $50 will go a longer way. You'll just need to verify on your first purchase, but they're legit.
As for packs, I love the ones I have right now. It really depends on what you like. I recommend getting at least one EP and one GP bundle that comes with 2 SPs.
For EPs, I have Get Together and City Living. I love the nightclubs in Get Together; they remind me of Nightlife in Sims 2, and that was fun. The club system is also nice, since it's very versatile. City Living's apartment life is fun, and the festivals are too. Karaoke is also a nice touch.
If I had to recommend one, I'd say get Get Together first. It has good value, and the new world Windenburg is pretty big as well.
For GPs, I have Spa Day, Dine Out, and Parenthood. I like them all too. I love having my sims dine out, and running a restaurant is fun too. Parenthood adds a lot to family play if you're into that. It's also fun to have sims go to the spa, and you can also have them do yoga and meditation.
I'd recommend getting Dine Out or Parenthood first, depending on your preference. And make sure you get the bundle so that you also get some SPs, if you like.
For SPs, it's really just a matter of preference. Each one appeals to specific interests. But I like Backyard and Kids Room the best. The water slide, puppet theater, and Void Critters are fun additions.
