Sex File: Should I have lied and said he's the best I've ever had?

That question, however jokey, reflects a degree of insecurity on your husband's part, so the smartest response would have been to confirm what he obviously wanted to hear

In a jokey, post-coital conversation, my husband of 15 years asked me if he was the best lover I'd ever had. I replied, "Well, there was X . . .", referring to a fling I had in my 20s. I was surprised by how much this hurt my husband's feelings. How can I reassure him?

That question, however jokey, reflects a degree of insecurity on your husband's part, so the smartest response would have been to confirm what he obviously wanted to hear and give him a light-hearted but reassuring validation of your sexual relationship.