informed decision： 明智的决定;合乎情理的决定。 因为我觉得“informed”基本含义是：消息灵通;指对各方面的消息能及时掌握。那么与决定组合使用，应该是在综合各种信息后作出的决定，会是比较明智和合乎情理的。 Ps:不过，英语单词和短语是没有绝对的固定意思。还是要根据上下文分析才对。 最好你把上下文一起告诉我们。

to be well informed = someone who is well informed on the topic at hand 消息灵通 An informed decision is made by someone who knows almost everything he needs to know before making that decision. Now what is that in Chinese?