I've always used Crank Bros. Candies on my mtb and cross bikes. Double sided entry and they have some float. I've never really had a problem clipping in or out.
I've been intrigued by these, too. I know they're really popular. I'd love to know more about the LOOK mtn. pedals that are pretty new on the market, but they've not been around long enough to have developed a reputation. I really like my LOOK road pedals.