What kind of bulbs are you looking at using? If you are using floros, there is no evidence that says either spectrum is better than the other. If you are looking at HID bulbs then HPS is going to give you what it gives you unless its a modified spectrum bulb. Some have used the modified spectrum HPS which is supposed to have more blue spectrum in it but the results are not impressive enough to shout about. Just make sure that you get the bulbs that are within the spectrum range of 2k to 3k and have the highest amount of lumen output per watt. The cfls don't have a high lumen to watt ratio but the T5s do as good as the MH for lumens and color but are a tad weak for flowering. If I had to use floros for flowering then I would use the T5 in the 2k-3k range and maybe mix 2-3 bulbs of 6500k in with them. Hope this helps