Should I trash copper or silver with Mine?
In Dominion, when playing the Mine card, you can "Trash a Treasure card from your hand. Gain a Treasure card costing up to 3 Coins more; put it into your hand.". If you have only Copper or Silver in your hand, then the choice is obvious which to upgrade. If you have both Copper and Silver in your hand, what are the pros and cons to upgrading one over the other?