For the World's Qualifier, the format is stupid, single elimination, meaning ... luck based format. So, obviously, the deck you really don't wanna face is ... FTK based decks.
The most obvious and dangerous one right now ... is Frogs (with Mass Driver). So, do you wanna main that DD Crow and at least have a chance of screwing your opponent's shit out or just waste your first turn and hope you get your crow in the remaining duels ... ?
This is a tough call, as if you don't go against Frogs ... that DD Crow is one hell of trash ... cause obviously the format is gonna be RULED by BF.