Adding 2 more lights to my room HPS or MH..?

I currently have 2 1000w HPS in Raptor Hoods in my Flowering room. I'm about to add 2 600w lights to the room. I am having trouble deciding between using mh or hps. Comments....thoughts.....?

My friend is using mh as his extra side lighting...and the plants look great...was thinking of copying.

Thanks