I have bikes with both SKS and Planet Bike fenders. Both work fine, but the SKS are clearly nicer looking and come with high quality Stainless Steel hardware. The PB fenders are cheaper, a bit easier to install, but some of the hardware is regular steel. I have the SKS fenders on my commuter and the cheaper PB units on my wife's bike and our cheapy tandem. I like the look of some of the fancy Stainless steel fenders, but they cost too much for my wallet, weigh a more, and and can still have some corrosion issues (stainless is not completely rust free. Any set of properly fit fenders will make cycling on bad weather days a much less unpleasant experience, but for my money the SKS's are my favorite on a good bike, and PB's get use on any low use/cheap bike.

Happy riding,
André