LEDs are better than either MH or T5. Sorry couldn't resist
But seriously, they are the future for lighting in our hobby. Only problem is up front cost. I am looking at eventually building my own array for my new 65 gallon and it will probably cost me $1100 to $1200 in parts. But that will come down over time as the LEDs get cheaper. Long term benefits are lower energy consumption and no bulb changes as the LEDs should last from 8 to 11 years depending on photoperiod. I'll have PAR as good as a 250W MH with no heat transfer to the tank. With more LEDS and tighter optics you can easily hit 400W MH PAR levels but then the build costs go up too. Final benefit is you can adjust the colour temperature anywhere you want it and the Cree royal blue LEDs generate great Fluorescence in the corals and if you can build and program a controller you can dim them for dawn/dusk or moonlight effects.