Favorites for me are tied between Late Night and Ambitions. I don't actually use any of the professions in Ambitions but it added so much new content I simply couldn't play without it (such as sculpting and tattoos). As for Late Night, it was the first expansion pack I ever got and I simply love cities, vampires, and making all my sims celebrities.
Least favorite is Seasons. I had a potato computer when I first bought it, and still vividly remember how bad the rain and snow made my game run especially in Bridgeport and Appaloosa Plains. I still hold a grudge against the pack all those years later, despite now having a decent gaming rig.
