As everyone who has had some experience with reef tanks knows, lighting is one of the most important aspects that can make or break your tank. A few things to consider:
Depth of the tank
LEDs, LED quality, power, optics
Metal halides, size, power
T5, Size power bulbs
What type of corals
The placement of the corals
Which one prevails is highly dependent of a number of variables, including those mentioned above.
T5s work great, many use them with excellent growth and results from sps to softies, the same can be said for metal halides.
LEDS are a relatively new product in reefing but again, same thing people have tons of success with them. What this comes down to is budget and what your plans are for the tank.
You can buy 2 bulb T5s that wont grow much or you can buy a 6 bulb that grows everything.
T5s are middle of the cost spectrum. They work well, have a fairly low energy cost and only need to be replaceds every six months to a year.
Metal halides give a very nice shimmer effect, but the running cost certainly makes this a luxury because they use a lot of energy. They also generate a relatively large amount of heat, to the point where it’s possible you will need a chiller but the bulbs only need be replaced every 5 months. Most people know they are highly capable with corals.
LED Aquarium lighting are the new kid on the block. Many people are using them these days and the equipement itself is improving in quality. Like with all advancement in technology there will be sceptics, but for every sceptic there are others who are having fantastic results with LED Aquarium lighting. They aren’t cheap but have a very low running cost and longevity.