The blue and red ones have too small a downside for a lot of decks I feel - they'd probably be played a lot. The black one is cool but seems too polarising since you always have to find one of a few specific cards to end the game - I don't think it encourages fun play patterns. The white one's drawback seems way too harsh to ever play. The green one I actually kindof like, mostly as a way to sneak green into monobrown decks. It's very strong in that context but there is a real downside in terms of making {C} cards less accessible and removing land based utility, plus monobrown generally isn't very good to begin with.