NiB is generally easier to clean after shooting, and not having a black BCG makes it easier to see the residue. IMHO, the action is a little smoother with the coating when it is lubed the same. Not enough to justify doubling the price, but if it were about 10 bucks more, I wouldn't feel too bad about paying a little more.
"Democracy is two wolves and one sheep voting on what to have for dinner.
Liberty is the well-armed lamb contesting the vote." - Benjamin Franklin
If you go the NiB route Fail Zero is the best out there. I've built with different NIB BCG's and they do loose the coating and discolor. My Fail Zero has 2k plus through it and it still looks new and still has a slick coating to it. I have regular BCG's and there not much difference other than ease of cleaning if it's a good quality coating.