I use LED (I’m a new grower, working on my 2nd harvest), and love the results and energy savings! I use 2 MarsHydro 300s for a 4’x2’ tent. All my research and results so far show 25W LED (TRUE wattage, for example, a MarsHydro “300W” only has 130 TRUE watts) per square foot. 100W/sq-ft for CFL (50-75W minimum). I have no experience on HPS or MV. I keep the MarsHydros 18-20" away from the plants, and have good growth with no light burn.
I also have a solo plant chamber with a TaoTronics 24W LED, which I’m pretty happy with, but they have a new 36W that’s a LOT better (better angle) for about $35 or so. And I use 2700K and 6500K CFLs for my incubation chamber, which give good results.
Those are the cheap-but-good LED lighting options I can vouch for. Several folks here have a lot more experience with different kinds of lights.