this is going to get troll flamed so hard, but I'll go ahead and get things started.
1.) Look for a reputable company based out of the usa that offers at least a 3 year warranty
2.) You'll want lights that use at least a 3w chipset, meaning the diodes will be driven to around 2.1w per diode. Leds aren't driven to full capacity this is what keeps them alive for 50,000 plus hours.
3.) Ask for a spec sheet from the company you're considering. Make sure the advertised wattage is the actual output wattage and not the wattage the light could draw if driven to full capacity - there is a huge fucking difference between the two and some companies advertise actual wattage, others advertise chipset wattage.
4.) Type of diode used, look for CREE, bridgelux, or Epistar - those are the three big players. Do some research to make sure the company actually uses them instead of just claiming to use them. There are a ton of people out there to rip off the consumer who hasn't done their research.
5.) I spent a lot of time researching leds before I bought the companies I had on my short list were (in no particular order) - Stealth, Hydroponics Hut, Pro Source, Grow LED Hydro. I'm sure there are other good ones out there though. In the end I wound up purchasing Pro-Grows from Hydro Hut, they've served me well.
6.) Number of spectrums employed - 2,3,& 4 band lights are out of date, most quality 2011 model lights are going to use at least 6 spectrums if not more. In addition to my Pro-Grows I also own a GLH 100w ufo that uses 12 different bands.
7.) Look for quality grow journals featuring the light you're considering and try to make sure they aren't just a smart plug by the company in question.
Hope this helps. Get ready for a bunch of people to stop in and shit on leds. That's what usually happens on this board. There is a journal in my signature line if you'd like to see what I've done with mine.