Wow that is interesting, so obviously just MH alone is better for vegging. Was the same strain used in the comparison btw the MH and HPS?i just took some good photos that show the difference.... we didn't partition off or anything, but the bigger plant was closest to an MH all its veg-life, and the smaller one was closest to an HPS:
the mh girl:
the hps girl:
note: we moved them to the same spot in the room to take the pics with, as you can see the mh girl is still standing just fine, where the hps girl is doing a bit of a lean because of the jostling when we moved her.
The 2 ballasts I have can be used for both HPS and MH.personally, if you're working with 2 ballasts, i'd get one of each.
the mh kicks ass at veg, but the hps is really where it's AT for flowering (or a combo of the 2), which i think is the more important stage between the 2.
(hortilux makes a good mh, and i think the hps we're running right now is by phillips? sunmaster makes a solid one too.)
alternately, you could get a dual arc bulb(both spectrums), but that can be $$$.... ushio makes an awesome one but it retails for like $180.