I've always kind of liked the tamas that were difficult or challenging to run! (Not so much anymore since I'm waaay to busy for that now unfortunately) The music star is one of my favorites due to how complicated it is, with the stress meter and pro debut especially.
I have a soft spot for the mix/meets/on tamas, really just any one of them with the mixing feature. It was extremely fun to run when the gimmick was still fresh, I ran my mix for over 50 generations when i first got it! It's such a fun feature, though I'm glad it's not a permanent thing in every single tamagotchi now.
I like the pix and I have a feeling it will be one of my favorites once I get a chance to properly run it... the battery life on it is so bad it's basically impossible to enjoy for me right now, especially with wanting to make use of it's camera feature. But I really love all the interactable aspects of the pix! It really makes it stand out compared to other tamas
