I'd also prefer hearing my environment. Don't think I've played music on the actual trails yet, especially since I can't really help myself but blast it when I do play it. But for the parts of the trails where you can relax a bit, go metal. SlipKnoT, Manson, Zombie etc. Otherwise if you want to really, really relax go with some atmospheric. Or best of both worlds, atmospheric metal like Abigail Williams lol