Ooooh, this is going to be tricky for me. I remember back in the day when EPs weren't that big a deal to me but Game Packs were everything. Now there's a lot of awesome EPs so it's hard to pick my three. I suppose it depends on what my mood is and what kind of Sims I feel like playing at the time. So all my answers are always subject to change, though I'm most definitely an Occult/Fantasy/Sci-Fi/Anything Weird Player. But I'll give it my best shot, lol.
Kits (Okay, I'm already having trouble choosing, lol):
CAS Kits
1. Goth Galore
2. Fashion Street
3. Prairie Dreams
Honorable mention: Silver Screen
Build/Buy Kits
1. Storybook Nursery
2. Secret Sanctuary
3. Wonderland Playroom
Honorable mention: Castle Estate
Stuff Packs
1. Paranormal
2. Spooky Stuff
3. Crystal Creations
Honorable mention: Vintage Glamour (I love a butler!)
Game Packs
1. Vampires
2. Werewolves
3. Realm of Magic
Honorable Mention: Jungle Adventure (Selvadorada! *Swoon*😍)
Expansion Packs (This one is just too hard, it's killing me!)
1. Life and Death
2. Enchanted by Nature
3. Horse Ranch
Honorable Mention: Island Living and Lovestruck (I need them!)