I think true love dances on that line of foolishness and stupidity far more than one could be comfortable. As helpful as using your mind would be when leaving yourself that vunerable, when you are truly in love, you mind will have very little to nothing at all to do with it. As love, itself, is a totally illogical emotion.
Short Answer: Your Heart
Mind. Speaking from experience
The heart because the heart leads to the right path.
Usually people have this dilemma when they know a relationship is a bad idea...be careful.
listen to what your heart tells you; your mind can deceive and play tricks on you.
You need both! You need the passion your heart provides, and you need the logic your brain gives you. Is the passion and love worth more than any hardships your brain can think of? Can you handle what your brain brings up, or will your heart be able to see past and trudge on with love? Only you can answer that.
In my experience, it's a judgment call at the time. If you allow your heart to lead, and you submit your mind to that, then know that you are taking a risk, and accept what the consequences might be. This is usually in cases where you don't have enough information to make a very solid mindful decision.
It feels good to go with your heart, but the heart doesn't always know what its talking about. So it would depend on who they are, and what situation you're both in.
I think the heart harbors more importance than your mind.
Listen to whoever you want, but in any case, you should always do what's best for them.