My two cents:
I used fluorescent lights for my first 2 months. I got an 8 bulb T5 fixture from hydrofarm. I decided that the 2ft long bulbs were enough for my setup(6 plants). I ran the lights for 24 hrs a day and the plants all got about 20 inches tall and about 30 inches wide.

Last week I started my 12 hour dark/12 hour light phase so my girls would start flowering. I purchased a 600 watt HID set up and got a dual bulb that is HPS and Metal Halide. The plants seem to really react well to this light and in 8 days have grown another 3.5 inches each and are really bushy.

Hope this helps,

BamaGrower