What the others said. There is no right height, just whatever works best for you. Most shredders and jazz guitarists actually hold their guitars from the hip to mid chest height to allow their fretting fingers to move quickly without putting strain on the wrist. Rhythm players like Hettfield who mostly play powerchords don't have to worry about huge stretches and fast runs so it is much easier to play down low. Then again, it depends on body mechanics such as the flexibility of your wrist joint and tendons, length and striength of your fingers etc. My $2.02c!