I've usd SPD and Eggs. I like the more distint clip-in clip-out feel of the SPDs, but overall I think the eggbeater design is better. The cleat engagement mechanism is extremely simple, they don't clog in mud, its impossible to vertically unclip (unless your cleats are worn), its easier to get in and out of, and all crank brothers pedals are compatable with road (3-hole) and mountain (2 hole) shoes (its just a matter of having the right cleat).

I use Crank Brothers Quattros on my road oriented bikes..those things are awesome. They have the simplicity of the eggbeater design, but a super stable platform, and narrower Q than other Crank Brothers pedals. For offroading, I just stick with the basic eggs.

Also I should add that CB customer service is awesome. I have five sets of CB pedals and I've had a few problems with bent axles and other parts breaking (usually from hitting logs and rocks) Everytime, I just called them up and they were happy to sent me whatever replacement part I needed. Once I had a pedal that wasn't engaging the cleat properly. They just sent me a new pedal...no questions asked.