Neopets is the only one i consistently return to at the same rate as FR. Nostalgia for sure, but there's also just so much to do and you are not desperately punished for disappearing for a few years. I have had long stints on chickensmoothie, but when the friend group I had on there mostly moved to skype (yes it was long ago) i just moved with them, it was never really the pets that kept me there.

I've tried a bunch more, most forgettable. Once in a while I'm like i should try any of the more realistic/breeding focused games like howrse or lioden, but they dont really encourage the creativity and character building that FR and Neopets does as the pets seem more to be like a resource than a pet idk i always bounce off again after a few weeks (likewise ive tried marapets, subeta and some of the other neopets clones but theres never that much to do to keep me engaged)

I think FR is consistently better than a lot of the other sites despite also suffering from "not that lot to do that isnt making your own fun" syndrome, probably bc the art is just really good and the world is very grounded + its not brutal to get pets you actually like looking at and the premium currency is very accessible