My *twisted* reasoning for Teferi's Puzzle Box as my number one choice:
Many, many and "Oh,..." so many times I've seen this card in the hands of *newbies* who have zero to no idea on how to use it. Since it's a
crap rare a lot of new players will most likely own one and put it into their decks regardless of focus or not. This card has destroyed me many times as a direct result of it being plopped down at the wrong time (both for me and it's owner). In fact, I am still waiting on a experienced player, that I know, to play Teferi's Puzzle Box, none have as of yet.
For this reason, I feel that T.P.B. must be a great card for casual players because I DO hear a lot of folks talking about it when it hits tha table but never a peep out of any tourney players
I've owned a few in the past and LOVE to trade it off a.s.a.p. Based on what it does to the game environment and the reaction on the face of the *newb* when they realize they have to do it, too, makes this card my #1 choice.