With over 300 played sims, that's a tough one, but I'd say Jophiel Ember, an angelic mermaid living on Sulani, is the prettiest female sim I've ever created in CAS.
https://abload.de/img/ts4_x64_2021-03-13_198udv9.jpg
As for the men, there's Jophiel's son, basically a male version of her who is also my simself's boyfriend, but I don't have a picture of him right now. Which is probably for the best, I wouldn't want anyone to get jealous. :p
The prize for my prettiest sim born in-game goes to Goldie Holle, a spellcaster from Brindleton Bay. This is remarkable considering that her parents aren't particularly attractive, yet their genes mixed so well that she doesn't even need any makeup. The only thing I changed about her when she aged up was the hair... and clothes, of course. You can't trust this game with randomly generated outfits.
https://abload.de/img/schnsterimspielgeborevii7e.jpg
With cats and dogs, it really depends on what breeds I find cutest, so I can't pick a winner here. But among the seven horses currently in my game, my favourite is probably Sphinx, this beautiful mare made by my mother. Look at her face, isn't she just adorable? <3
https://abload.de/img/signal-2023-08-05-21-80cuv.jpg
