Nikon NC Filter or B+W Clear MRC 007 Filter
I own both as well as many others (Heliopan SH-PMC, Hoya HD, Marumi Super DHG, Hoya Pro1D) and suggest to buy the cheapest of the bunch as they perform similar. With such good protectors you cannot see any difference without comprehensive testing and if you perform the testing, the differences are still subtle (in flare or little bit warmer tones, not in sharpness). I have no problems with cleansing of any protector filter, so that's also not the reason to prefer one over another (it is interesting in case of CPL filters). Some coating are more easy to scratch than others, but once again have no problems with either the Nikon and B+W. The difference is in toughness and material of frames, but I've found Nikon NC to be solid, so the Nikon would be my choice (and is my current choice because it is dirty cheap at ebay and found no reason why pay more).