I have a couple favorites. My favorite v2 character would have to be Ichigotchi ( ). Then out of v3 I like Urutchi (although they changed the name to wooltchi. it looks like a sheep) and dorotchi (it looks like a ghost). These were both v2 characters, but I still like them a lot.
Nyatchi from v3 seems pretty neat too, but I haven't gotten it yet.