Well I will throw in my 2 cents...

I use T5s for veg and I will use nothing else. Some growers that I talk to say that T5s will not promote a hearty enough plant but I think that this is not true!

Plants love T5's! They veg fast and get strong for a fraction of the wattage. I use 2 4' long Sunblaze44 T5 arrays. The reduced heat is the biggest plus and you can spray your plants with almost any fungicide/pesticide/inocculant without any burn!

I do believe however that yields are reduced when flowering under T5. The lumens are just not enough and the light diffuses to quickly especially if you are trying to penetrate a deep canopy.

I have 2 flower rooms. One has 4 X 400 watt HPMH full spectrum bulbs and the other has 3 X 600 watt HPS using Hortilux's Super HPS bulbs. I love them both because they each have a lot of upside. Ultimately I want to get both rooms to 4 X 600 watt Super HPS lights. T5's can't touch that!!!!!