Well, I wouln't reccomend getting a v2 since they're hard to find these days (including v1s) But if you get a v3 or v4 it's pretty much just which you like better, or both!
I recently just got my v4. With it being my first tamagotchi, I was hooked on it. (still am!) Tamatown for the v4 is also very easy to make gotchi points off.