Hey there! (I also suggest moving this discussion into The Sims 4 Expansions Pack thread for more visibility)
It really depends on what you value or what you think might be fun. However, before you choose a pack I would recommend watching LGR reviews, as he’s pretty honest and gives pretty good criticism. Think it through well and have fun with choosing an expansion pack!
I personally love Seasons because it adds so much to whatever game you’re playing. Unlike the other expansion packs which concentrate on mainly a career, place or additional things to sims that are really optional in some cases, Seasons suits every play style and gives you some things to marvel at. I love taking screenshots of the world and like how it makes the game all the more realistic. Plus you have all the cute interactions like snowball and mud fights and jumping around in leaves!
I also really enjoy Cats and Dogs for some reason even though it only comes with cats and dogs. They add more realism to the game and if you’re a pet lover I think the whole pack is pretty cute.
Good luck with choosing and happy swimming!