Depends on what guitar I'm using I guess...usually my off-set body guitars + my petite size would make it look lower but it's the same as FGL's preference lah...the crotch level *lol* Just tilt the neck higher for better access lor 
I'm impressed by those punk rockers who can do like 1000-alternative-picking palm mute notes per min with their guitars slung at the knees and doing those split jumps!
For my jag, would be this height:

I'm impressed by those punk rockers who can do like 1000-alternative-picking palm mute notes per min with their guitars slung at the knees and doing those split jumps!
For my jag, would be this height:
