I think it depends on your play style. I personally find the relationship mechanics in Growing Together really fun, obviously it could use some more work. CAS and build/buy items are cute but nothing to write home about, though I really like the tree house.
I've played a bit of the horse ranch and it's a little meh for me, maybe I haven't played it enough yet. The goats and sheep are super cute, they bounce around every where and I lose it every time. It's been fun training the horses but entering events are rabbit holes, I wish that aspect was more interactive.
Some new aspirations in both packs, GT has new kids aspirations which I think is fun. There are some new traits in horse ranch as well.
I'd rate Growing Together higher than horse ranch personally there just seems to be more in game play mechanics.