I didn't vote, because I only have Dine Out, so I would be biased haha. (Although I do want Spa Day one day).
I really enjoy putting restaurants in my game and sending my Sims out for romantic dinners, friendly get togethers, and even special occasions (you can ask a waiter to bring out a birthday cake). I think that Dine Out works really well with other packs too, for example, thanks to Snowy Escape I have a beautiful Japanese restaurant.
My question to you would be where do you think you're most likely to want to send your Sims? If you play families more often, then you might want to send them out for a lovely meal together, but a young single wealthy Sim might prefer treating themselves to a spa day.
As for BB and CAS, I rarely use the Dive Out BB but I do use the CAS alot, especially the female hair. It also adds some more modern formal wear looks that aren't long dresses.