LED aquarium lighting has actually drastically come down in retail cost over the past five years. A led light fixture that may have cost $2500 just five years ago, may now be well under $1000, giving both Metal Halide and T5 fixtures a run for their money.
Also if you think about the higher long term costs & other factors associated with maintaining Metal Halides and T5's, one may consider LEDs even more. Some of the higher costs & issues, as we all know, include: expensive bulb replacement (semi-annually or annually), accidental bulb cracking, hazardous bulb disposal, a higher rate of stray electrostatic electricity is produced, high wattage draw (equates to a higher electricity bill) and a strain on home outlets, and the heat factor, which typically means having to run a chiller (more electricity and more strain on the home outlets). Not to mention hobbyists who have burned their hands by accidentally touching a metal halide or T5 fixture (even after it's turned off) when moving it for maintenance or to make height adjustments. To me these are all great reasons to consider running LED.
I've read tons of debates. And I've found that most of the hobbyists who are negative towards LEDs, have never actually ran them. I also can't recall that I have ever seen where someone has switched to LED, and gave them a bad review. Typically, once someone switches they like them. There's no doubt that Metal Halide lighting and T5 works, and can grow great corals, but I've seen where a lot of reef-keepers, including myself, are starting to really like the LED for growth.
In conclusion, I'd say to the hobbyists looking to upgrade their aquarium lighting, to go LED all the way! No doubt.