Anything Chibi is top tier, especially the experiments. I think my favorites have to be:

This is hard, so I guess I'll stick to the common colors... Experiment wise, either or . Regular, easy-to-get pets, would be either an Ontra, Chai or Wyllop.

Cutest colors are sweetheart or nostalgic, they make almost every pet cute and cannot be counted due to the inherent unfairness of making someone pick a favorite.

tentacle pupper forever

Devontis are super cute!

And, of course, scribble pets!

hands down the cutest

2 cute 2 poot

I mean, I'm biased but...

I personally think the Malticorn, Legeica, and Hikei are the cutest ;u;

These:

Depends on your preferences, of course, but personally, I think Chibi, Nostalgic and Sweetheart are probably the cutest.

OR you could go with something that's both cute and spooky.