Guys, the opening three things are examples, not the main question.
The QUESTION is, "How do you judge these decisions"? What is the thought process you use to decide, "Do I take a less-good card now, because it will not be available soon," versus "Do I take a more-good card now even though I'll have more opportunities to buy it later"?
Trying to answer it for myself, I suspect that the answer depends on whether the contested card actually combos with itself (like Minion or Nobles), or whether it's just a useful, good card (like Caravan or Fishing Village). The former seems more likely to be worth forgoing a "better" card to buy, both to increase the chance that your deck will start consistently firing, and to decrease the chance that your opponent's deck will start consistently firing. The latter seems like it's less vital that you end up at least 5-5 rather than 4-6.
But how about the amount of the contested card left in supply, or the ratios that you and your opponent have? Is it more or less good to decline the contested card if you already have a lead in the contest? Like, if you have 3 and your opponent has 2, is it better to lengthen your lead or to say, "Well, if he catches up, no worries"? How about if there are 3 left in the supply versus 7 left in the supply?
How about if it's earlier or later in the game?
I can see arguments in all directions. Like, "Sure, I don't need to worry about getting every last Minion, so since I'm ahead, I'm okay with letting my opponent catch up a little," versus, "I have a decisive Minion lead, I can consolidate that by preferring Minions to other, 'better' cards and making sure that my opponent simply can't put together a Minion engine."