Get Together or Pets?

GT for sure.

If you’re not THAT into pets I don’t recommend Cats&Dogs. Cats&Dogs is, imo, for real life pet owners to enjoy the furry company in game. It’s not at all a FUN pack, it just simulated the cats and dogs and it’s good in that way.
Get Together is a must have.

Since you're saying you're a family player and you love City Living, I think Get Together is the best option for you.

As much as I love Brindleton Bay that comes with Cat and Dogs, and all of its build mode items, I'm going with Get Together also. Windenburg is a lovely location with a lot of options, and a lot of good stuff for interacting with other sims. Plus new things to do when going out and about. I've found that Get Together also actively does encourage you to have your sims go out on the town more than otherwise, which is good for players like me, because I tend to get so focused on the household goings on that I forget that there are so many places to go.

That said, if you do want the addition of cats and dogs to make your family play feel more realistic or complete, by all means! The town is beautiful, the build items and CAS items I think are absolutely fantastic. Cats and Dogs is worth it for that alone, to me at least. But if you want to focus on interactive things that don't revolve solely around pets, then go for Get Together.

I also absolutely LOVE City Living. More than I do Get Together or Cats and Dogs.

You're probably better off with 'Get Together' (at least for now). Despite the recent patch, pets are STILL buggy and VERY glitched. They're constantly filling your Sims' queues with "pet me" interactions. Also, they constantly force your Sims to stop what they're doing (especially during meals) just to pet them. It gets highly annoying when your Sim is eating, but needs to put away their food into the inventory, stand up, and walk over to the cat/dog... just to pick them up and/or pet them. This happens consistently.

So far, 'Get Together' doesn't seem to have any issues currently. So yeah, I would suggest that expansion pack for now.

Edit: I don't know if this means anything, but I think it's also worth noting that I was someone who literally bashed 'Get Together' when it was first announced... but it ended up becoming my 2nd favorite expansion pack for Sims 4 (Seasons is #1).

I've never been into get together, it just seems to be all about nightclubs and partying which just isn't my thing, I don't really see it as a pack for family play. I'd suggest cats and dogs if you're a family player, Brindleton Bay is a great world for families and with the addition to add pets, I haven't had any bugs with the pets .

I love family play and I honestly can't imagine my game without GT now, it helps a lot with family gatherings (now celebrating holidays) with big, multi generational families.

GT is actually perfect for family play. You can start a club for just your family and do normal things around the house to quickly gain perk points such as watching TV, doing homework, using the toilet/taking a bath, etc. Once you call a gathering, it will keep going until a Sim or Sims leave the lot without others (this doesn't include work and school).
Toddlers can't be included, but that's perfect because they need to learn potty training and one of the management perks would interfere with that.

The perks are very helpful.
Rally the Troops gives all Sims in the club a boost in hunger, bladder and energy. You can use this over and over to keep your Sims going. All they need is to shower/take a bath before work/school.
Network gives a boost to the performance meter for work so it doesn't take as long to get a promotion.
You can buy vibe perks that are great for helping to achieve aspiration goals. Set the club vibe to focused when your children are trying to complete the homework requirement for the mental aspiration. Set it to playful to complete the requirement on the jungle gym for the motor aspiration. Etc...
There are perks to build skills faster.

Once I discovered that you could have a family club, I learned that it could help right the wrong of a Sim leaving the lot at night when the others are supposed to be sleeping. Since the actions are dropped from the queue, they don't get their sufficient sleep, but if I call another gathering and use Rally the Troops a few times, everyone can be good to go for work and school!

Since you say you're not that desperate for pets and enjoy family play, I'd say Get Together is the better option.

Get Together is such an underrated pack, it adds so much new gameplay and the club system is really cool.

Pets are fun...at first. It feels more like a chore after awhile tbh.