To me, it's definitely Strangers. My main issue with L&D is that it sounds really touched up. The production on the not played songs on Strangers (Mather Mary and This Kids) sound so much actually more live than Southbound.
There's some great songs on L&D, but for me, most of my favorite Thin Lizzy songs come after L&D, and I muchly prefer Life:Live over L&D.