Well if ur willing to spend the $$$, go with Metal halid. U will need to have it in a enclosed vented light fixture because they will get very very hot..if not that then I would go for a set of floresents tubes...really depends on how much u wanna pay
I have a 150 watt mh & hps and also a 250 watt mh & hps. Last time I used the 150 and results weren't the best. Now I have purchased a 250 watt and just put it in bloom so my plan was to stick wit he 250 but now I'm wondering if I should put the 150 in tre for a 400 watt total?