Mew and Mewtwo
Mew and Mewtwo have been my favorite pokémon in the series since the very beginning, since the first time I saw them in the opening of the Pokémon Anime when it first aired in the states. I've been collecting Mew and Mewtwo figures for some time now, though only recently have I been able to get my hands on the more rare, japanese only items. I really can't say which I love more, Mew or Mewtwo, I like them both equally for different reasons, plus seeing them together usually has some of the most adorable and hilarious results.
To me, there's something a bit symbolic about the two characters themselves, one natural, one created; related but not directly. For that reason I prefer to collect the two in pairs, sets that feature both Mew and Mewtwo are the things I search for the most, and anything that that features Mew and Mewtwo in the same figure are picture are some of the things that I consider the most prized and truly are the best symbol of this specific collection as a whole.