My most fave starter line of all time is obviously Oshawott and its evolution line due to that awesome samurai theme they have, and not to mention my fave of the starter types, Water! None of the Water-types have ever disappointed me, maybe Froakie did when it was first revealed but its design grew on me. 6th Gen's starters all look pretty awesome in general so I'm hoping they get awesome evolutions, especially Froakie due to my preference for Water.
Least fave, definitely Charmander's line. The reason? Charizard is soooooo overrated and also didn't like the way he was handled in the anime, especially the disobeying Ash part. The others aren't too bad though, I don't even mind Emboar or Meganium but they didn't live up to my expectations, at least I loved most starter designs.