i’ve only ever had poppy in new horizons, but i personally would choose lolly! i’m biased, but she’s one of my top 10 favourite villagers and i adore her with all my heart. you honestly can’t go wrong with either of them, though! ^~^
I've had both, and I like Lolly a bit more. Her expressions are just so adorable. Poppy has a pretty awesome house interior, though. Agree with the others that it might depend on which one goes with your island theme or colors more.
I've had them both on my islands and earned their photos and they are both lovely. I think it depends on the aesthetic of your island. Poppy has that lovely autumn theme home and Lolly's home is a more normal cat-next-door kind of place. Ditto for the exteriors--Poppy's is fancier and more elegant while Lolly's is more basic. Lolly's name in Japanese is Ramune, a popular soda. When I had Lolly on my island, Raymond was also there, and once in awhile they'd do yoga in the plaza together. It was very cute.
Such a tough decision.. I have had both cuties in my towns... however since I am a cat lover I am going to have to go with Lolly on this one. She's the perfect little tabby!