Which one of this packs is essential to your gameplay?

For kids who live in apts the small pets is a must as I hate trying to have dogs and cats in apts - it is such a pain to take them out and kids need pets. In Sims 3 it helps with their homework and scouting even. But technically having all packs is a must for me. I use everything as I play a lot of households usually. That little Hedgehog is simply adorable.