I personally prefer Spa Day and I actually feel it offers much more than Dine Out. (My personal opinion, please nobody come for me.)
In my opinion, Dine Out really doesn't offer much other than
- Resturaunts
- The ability to own and run a resturaunt
- A few new recipes
Sure, the resturuants, even ones you just plop down from the gallery are super custimozable. But in comparison, Spa Day offers
- Spas
- New Skill (Wellness)
- Multiple new game play objects (meditation stool, massage tables, yoga mats, sauna, incense)
- Yoga classes which gives you two ways to use yoga (in the spa and at home)
- Mud Baths and Bath Soaks which can be used in any bathtub. At home or at the spa.
- New Death + Woohoo location: the sauna (I'm not sure if this is something you're interested in but thought it's worth mentioning anyway.)
- New recipes
- New Fish for the aqauriums
As far as CAS goes, not only does it offer almost twice as many options looking at the number alone, but I also feel Spa Day is a lot more versitle than Dine Out. All you really get with Dine Out is a few options for formal wear or for resturaunt employees. But the Spa Day stuff can be used for every day, atheletic, swimwear, and even hot weather. I don't remember if the sweatshirts are tagged for cold weather, but you can use the clothing for a lot.
Build-Buy I don't have much of an opinion on, since they both have a more modern style. But I'd still give the point to Spa Day due to the the lotus flower themed items and the overall zen aesthetic. And because of the fact that a good number of those items are actually functional (ie all the gameplay items I mentioned.)
Plus, as others have mentioned, Dine Out is much more buggy as well. But even if it wasn't, I'd still pick Spa Day.