You can't say that "Silver is a good card in X games", because it's a good card in the early game in all games and becomes junk in the late game in most games. Often the correct play is to buy some Silvers early and trash them later. When you're thinking of buying a Silver, you have to take into account how much it boosts your deckbuilding speed early, and how much of a problem it's going to be later, and is there a way to get rid of it without losing too much momentum.