Well, they generally are concidered tighter and there are other things attributed to them, like being more scooped, but in the end, at least with BKPs, it comes down to the wind and other factors. A ceramic done well can be more middy than an alnico.
So what I am saying is that I do not see a real reason for prefering ceramic necks, most reasons that will be given are only general beliefs that donīt hold true, I think.
Not to say that there are no differences at all, but they are not that big. A pickup should be picked for the sound it produces, not because it has a ceramic or alnico magnet.
