i use both, MH for veg, and HPS for flower. i'll tell you that the mh definitely makes a difference over the HPS for veg. I have done HPS only grows, and the plants don't look quite the same when I'm ready to flower as they would had I used a MH.

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August 7, 1765: "--began to seperate (sic) the Male from the Female Hemp at Do--rather too late."
George Washington's Personal Diary