Ceramic magnets tend to give a more cutting and aggressive sound so the bass becomes more articulate. This is of particular use when you have a mahogany guitar, which tends to be bassy anyway. An Alnico V magnet produces a warmer tone and always seems a little more rounded to me so these tend to be used more on guitars that are a little brighter in nature. Of course, they can be mixed up in a guitar to produce different tones and effects, depending on their purpose, hence something like a Cold Sweat pup is ceramic for the bridge version and Alnico V for the neck version. The fact that your guitar is alder has led to the number of suggestions you've had that are Alnico V based. There is a sticky posted on the forum that tells you more about magnets and their effect but I think that essentially covers it for what you're after.
