Efficiency can be determined simply by the reward you receive at certain mana costs (Counterspell and Cancel do the same thing, but Counterspell costs less), the total payoff you receive from a single card (Hull Breach and Decimate are both good cards, but Decimate usually covers much more ground), or the payoff you receive in conjunction with other cards (Anointed Procession makes other token production cards completely absurd if unchecked, which is usually better than adding one more card that simply makes tokens like Spectral Procession in a token strategy)
Scry 2 draw 2 is better total value
He's written for Rock Paper Shotgun, The Big Issue, GamesRadar, Zam, Glixel, Five Out of Ten Magazine, and Playboy.com, whose cheques with the bunny logo made for fun conversations at the bank
Base Set Pikachu - Trying not to put more than one card from the same era on this list, but you cant deny Base Set Pikas cultural importance and relevance