Jesus....people get so worked up over this stuff. Here is a chart of the pros and cons:
LEDs (assuming a 280 watt led is equivalent to a 400 watt hps):
Pros: less heat, less wattage for same output, slightly longer life (yes only slightly, sadly. there is a huge push right now to extend led life since they dim quickly)
Cons: much more expensive per wattage, spectrum issues (some wavelengths are hard to obtain), less intensity (unless measured watt vs watt)
HPS:
Pros: cheap, intense, spectrum more "filled" (i.e. more balanced)
Cons: heat, shorter life, lots of energy wasted on spectrums that do not play into photosynthesis (inefficient is the word)
Up to you to decide which is better. I dont think there really is a better but I have to say, in every pro/medical gro op Ive seen they use HID's instead of LED's. Not saying HID's are better, but I think the cost is the defining factor. It doesn't take linear algebra to see that a 280watt led for 290 is much more expensive than a 400watt HID for 120. In addition, LED's dim quickly: dont be fooled by the 50,000 hr life expectancy. high powered led lights dim by 5% after the first year, unless kept at cool temperatures. when speaking of the temperature of leds, im talking about the led diodes themselves, not the fixtures. Currently, people have been trying to immerse LED's in liquids to cool them off through heat exchange.
Another problem with LED's is that once they dim, you cant change the bulb. With HPS and MH bulbs u can simply order a new one. Therefore, i think the real question is how much are you willing to pay? your energy bill may go down, but you can't used your LED panels for very long either because they WILL dim. So, i think a lot of large grow ops have realized that it just isnt cost effective in the long run to have LED's. Though, for a small, stealth sized grow, maybe having little heat emission is a necessity.