I'd say Cats and Dogs was the one I was the most excited for. I loved the New England feel of Brindleton Bay and the cats in particular were something I looked forward to. I made a lot of pets those first few weeks, playing with the colors and patterns. I remember really liking the CAS and B/B as well, as they were styles we didn't have at the time and filled a gap. I also ended up really loving Island Living, though I wasn't initially hyped for it until after a bunch of information had come out.
Most of the EPs haven't made me super hyped, but a lot of the Game Packs have. I love Occults and weird/fantasy/sci-fi/supernatural gameplay so much, and many of the GPs just hit it out of the park for me. :)