I mix and match. I usually always own the EP's except for in the sims 3 because I didn't really care to get Showtime and Into The Future. I also didn't really buy stuff packs for the sims either except for mansion and garden stuff in the sims 2 and the free stuff pack I got in the sims 3. This time around I own all EP's and GP's so far and only buy the stuff packs that interest me, and I only recently got Spa Day because it didn't really appeal to me at first. I guess it really just depends on what the pack offers and if I feel I'll get my money's worth from it.