You will most likely get more dense buds with the hps but it's going cost more in electricity and give of more heat. Nowadays I stay away from hps cos my setup is to small and getting rid of the heat is a problem for me.
A 600 HPS will eat LED lights for breakfast.
As long as you are able to control the heat and don't mind the extra running costs of the HPS, I would definitely pick the 600 HPS over the LED.
Cheers, Organoman.