I'm more of a form-follows-function kind of guy, so I just use what I can get at a reasonable price, which is usually something fairly new. The plastic Planet Bike fenders get good reviews, and they look fine to me. I have SKS Chromoplastic fenders on my Bianchi, and they work well and look nice. You can get Bluemels on ebay, but you'll pay a lot. The fancy ones, such as Velo-Orange, look really nice, and I can understand why someone would pay extra for them.