I would say that an interesting decision is one where there's reasons to choose either way. And that largely depends on the context of the decision.
If I ask you "do you want chocolate or vanilla ice cream?", and you absolutely loathe chocolate ice cream, that's not an interesting decision. If you are fanatically pleased by vanilla ice cream, it's not an interesting decision. But if you like both, even if you like one more than the other, it's now an interesting decision, because you have to weigh both options and make a determination on which option is best in the current situation.
Interesting additional point: if two options are found to be equally correct choices, then it's just as uninteresting of a decision as when one option is obviously correct. It's the valuation that makes a choice interesting, and the challenge of figuring out how to determine which choice is correct in an unpredictable situation.