I guess I'm in the minority here? Because I much prefer Cats and Dogs over City Living, in fact it is one of my favourite packs - and not just for the pets either, although they are really cute and versatile. Brindleton Bay is my favourite world so far and there are also lots of really lovely CAS and build items. I couldn't play without it now.
I do like City Living, but it's probably my least favourite EP after Get Famous. I'm not much of a city girl, but it is nice to play there from time to time, and I do like the festivals and singing skill, which also works well with Get Famous. Honestly I don't think you can go wrong with either pack and what you prefer will depend on your own play style. I recommend checking out the SimsVIP or Carl guides and other reviews if you haven't already done so to see which appeals to the most at this point in time.