Just on my own experience here is what I think of the former and new light technologies,
1. Metal Halides really intense lightning which have more than proven to work,
PROS,
Lots of lights
Different Kelvin types to choose from
More than proven that they work
All corals will grow under them.
CONS
Power eaters
Heat transfer
Bulb change every 6 to 12 months.
Space to hold ballast.
2. VHO/HO Lights, used for main or supplemental lightning, you can choose from a variety of colors.
PROS
Cheap to maintain
Proven to work
All corals will grow under them, depends on tank height or coral/clam position.
CONS
Maintenance, as you have to change bulbs each 6 to 12 months.
Power consumption (Not as high as MH's)
Heat transfer (Not as much as MH's)
3. LED Lightning, new technology offered by everyone now, but few manufactures can be trusted to really put out what they offer.
PROS
Low power consumption
No heat transfer.
Dimmable (Not all fixtures)
Nature Effects, as thunderstorms and clouds passing by (Not all fixtures)
Many research and development being invested in this area right now.
Upgradable (Not all fixtures)
Require less space as no ballast needed.
LED last 50,000 hours (at 8 hours per day, they last 17 years)
CONS
Expensive
Still haven't proven themselves, though, many successful coral stories around.
As I see it, many MH, VHO/HO and PC manufacturers are beginning to turn their interest to LED's I think that any of them who aren't most probably will be out of business in the short term (ex. IceCap).
Still, LED technology is really expensive, at least the fixtures that really have proven to work, and the return of investment can take years over common or former lights.
Nevertheless, with so much research and development around LED and so many consumers beginning to acquire them, it's not that far when we see a price drop on these.
As stated above, these lights mentioned above are from my own experience and not through others comments.
Please feel free to correct me in any way