I had the Look Deltas on my old commuter, but now have Look Keo 2 Max composite on the new commuter/tourer and the Look Keo 2 max carbon on the best bike.
I don't have much other experience to be honest but i find the Keo 2 max a really good pedal with a large surface area, especially if you're already used to the Look stuff. There's not a huge weight difference between the composite and the carbon, but if you shop around you can get the carbon for not much more than the composite... I just decided there wasn't much point getting carbon for the bike that's going to have weight on it anyway, but obviously is nice to have it on the carbon frame. I think I paid about £70 for the composite and £85-£90 for the carbon.
Also, if you do get any of the Keo pedals, if you invest a tenner in the cleat covers and get in the habit of putting them on, it really improves the life of the cleats.