Just like rjalda, the v2. I love the selection of characters, i love how some of them are old, some new. I think tamagotchis have become something incredible, but i prefer the more vintage, animal-based characters (as opposed to humanoid).
I like how care clearly affects their growth, but there seems to be some randomness to it as well. The entire of notion of the discipline meter, and parents affecting a child's growth is also an entire factor.
The games are simple, and i enjoy the overall simplicity of the v2.
I will always have a a deep love for the v1, as it came out during a really sad time in my life.