"Het is het belangrijkst dat je naar je hart luistert."
Translation:It is the most important that you listen to your heart.
That is terrible english.
"It is most important that you listen to your heart." "It is the most important thing to listen to your heart." "The most important thing is to listen to your heart."
Which of these is it supposed to be?
I think your first and third sentences are the best options here. In Dutch you wouldn't use "thing" (ding) in the sentence, so for translation purposes, and in order not to confuse people, your first sentence is probably the better choice.
I'm thinking about this again, I guess you can use "ding" in certain Dutch sentences, but generally only when it talks about a choice or something tangible. Example: Het belangrijkste van deze twee dingen is de liefde = The most important of these two things is love, or Dit ding is het belangrijkst = This thing is the most important.
I don't think this is a good translation - I can't imagine a native (at least British) English speaker using this structure. moparmike's alternatives are the ones you would use.