I don't really play my games on a pack by pack basis, but rather sprinkle things throughout and incorporate specific gameplay elements as they come and when it seems fit, depending on the storyline I'm playing out. If I'm playing a Sim who is super into saving the environment and conservation, I'll have them do the Eco Lifestyle and Island Living activities, but I typically play in Sulani more for the beaches and island events. If my sims need extra money because I decided to make them work for it rather than using motherlode, I might have them work odd jobs or level up their art/knitting skills to sell their creations on Plopsy.
Occult gameplay is my main playstyle however, so I definitely get a lot of use out of Vampires and Realm of Magic. I have at least one spellcaster and one vampire (usually multiple of both) in every save. My spellcasters typically practice magic and learn new spells a few times a (Sims) day. And quite a few of my sims have made friends with one or both of the Vatores. Caleb even offered to turn one who he become very good friends with, which I thought was adorable. (taking the phrase "friends forever" to a whole other level)
One of my current favorite couples is actually a vampire and spellcaster couple and I just love them together.
I have played with the Veterinarian career a couple of times, but if doesn't fit my Sims' story, then they just own pets. (I'd say about half the Sims I create are pet owners.) And I especially love giving them to spellcasters and binding them as a familiar.
