Clichéd as it sounds, there is a big chance you already know in your heart which relationship you wish to pursue. Perhaps you are hesitating because the other sounds convenient/socially acceptable or something else. Try to clear your mind of all externalities and concentrate on what your heart desires. Usually that relationship makes you the happiest. There is no guarantee you won't regret letting the other go sometime in the future. But regret is a part of being alive.