MH is so much less productive that there is really no compairing the two. if u have two setups next to eachother...u will see a HUGE difference. MH should be only used as an extra light source for lumes or maybe red's in a florescent situation. HPS is unsurpassed for all types of indoor growing.
I assume you are confusing the two? MH gives off a supplemental red light? I thought it was higher in the blue spec. than that of a red, and HPS is highest in red. so why would one use a MH for reds while growing with flouros?