Led Zeppelin by far. Now don't get me wrong I love AC/DC. The rhythm & lead playing of the Young brothers is classic three-chord fury, taking the fun loving simplicity of 50s rock 'n' roll and amplifying the hell out of it. But there isn't much more to their music than that. Zeppelin have some very complex music, and a level of sophistication to their sound that Young, and co. never recreated. Again, i'm not slamming AC/DC, their simplistic approach worked extremely well for them, and I enjoy their work. But Led Zeppelin's complexity, versatility, innovation, and unbelievable musicianship make them a better band.