Which kind of mountain bike pedal is most suitable for racing? It needs to be pretty light, but also durable to be able to resist a tough race.
I'm assuming we're taling clipless since we're talking racing. I've owned a number of SPD pedals and always found them lacking. I prefer Time Pedals and raced x-country on them for years. I own a pair of Alium's. When I bought them (5 years ago) no SPD kept as clean as they did. Speedplay and Crank Bros are also supposed to clear mud well but I've never tried them.
Ultimately this is a personal preference. See if you can get on a few different pedals at your LBS and read some reviews in magazines and on forums.
I have had SPDs and eggbeaters, and I love the Crank Bros eggbeater pedals. I've found them to be way better than SPDs. You can clip in on four sides rather than two, and in my experience, they're easier to clip out of in emergency situations than SPDs are.
Also, unlike SPDs, eggbeaters don't have flat surfaces, so you're less likely to slip off if you're trying to get back on after hike-a-bike sections of muddy trails.