If there is one flat out there which is the best by far for all types of riding then I've yet to find it. Some ultra grippy, massively wide ultra burly pedals are just too heavy for an xc bike and obviously some of the lighter pedals simply aren't suitable for dh racing in heavy mud. 5 10s are simply the ultimate, AM 40s have their good points, both are vastly superior to any skate shoe. Imo 50/50s are dirt, v12s are grippy but don't feel nice, easton, burgtec and straitline are pretty heavy for the money.
I like a flat as opposed to concave pedal myself, azonic x frame are really nice if a little small. Reasonable weight too and cnc'd. If I had the money I'd like to get my paws on these….