I got them all on sale, but the only one I'd go back and pay full price for was Get Together - it was the one I was least excited about and the one that ended up being my favorite, oddly enough. I love the club system, the world, and all of the new activities.
The other ones aren't bad - I quite like the scientist career for Get to Work (though I'm not a huge fan of active careers in general) as well as the aliens, and the festivals in City Living are great for building skills more quickly. Cats and Dogs is probably the one I've utilized the least (but only because my computer was stolen right after I got it and I haven't played as much since I've gotten my new computer). The Pets expansion has never really been my favorite expansion though - so that may be part of it. The vet career is fun, though.