Hi BudMan. It depends. Many are able to get 1g/watt using good LEDs, sometimes more. Most grows I've seen are around .75g/watt and some less which is about on par with HID lighting. The variation in quality from the major vendors is a big problem LED shoppers face, so rather than invest in something that may or may not work well, HPS is easier, has a proven track record and is much, much cheaper. There's no simple answer for which panel to buy, unfortunately. I'm sure someone can recommend a few good places to start though.
If you buy enough LED lamps you can come close to the best HPS bulbs, but the price of admission is quite high. I remember knna saying that you'd need 700w of high quality LEDs to equal a 1000w HPS, and that's assuming you build it yourself with good attention to thermal design and current. That would cost upwards of $2500.