The Boggs 8 hour mountain bike race confirmed my suspicions about which mountain bike fenders work best.
Ive tried quite a few different front and rear fenders, and after doing 5 wet and muddy laps and seeing numerous fenders broken on the side of the trail, its clear to me which fenders are best.
For the front of the bike I recommend the Planet Bike BOG front fender. Ive tried the SKS fenders and they dont last. They make great rear fenders, but after seeing 4 SKS Shockblade fenders on the side of the trails at Boggs, I can confidently tell you to buy a Planet Bike BOG front fender not a SKS front Fender.
As for the rear fender, you want as few moving parts as possible. When your bouncing down a wet trail any parts on the fender than can work themselves loose will do so. That means I prefer the SKS X-Tra Dry rear fender over their X-Blade rear fender which has many more adjustable parts.
T.H.E. also makes some good fenders, but they arent as easy to put on and take off as the BOG and the X-Tra Dry are.