What's the difference? Is the gain on ceramic bigger or not?
PS: I don't know what to say, but I only ask for those pickups difference in general.
This may not help a lot, but here is one person's opinion + facts about magnetic cores: sonicwrench forum
So like a lot of components in musical instruments, which is "better" depends on what you want for sound output.
Ceramic magnets do produce a stronger field, but that alone doesn't actually change the sound, it just increases the total output (which, of course, will change the sound if you thereby drive an amp further into distortion).
What's more relevant is that Alnico is magnetically "softer" (It has a higher reversible permeability) than ceramics, i.e. it changes its field more when affected by the string's movement. This effect is not very strong, but it notably influences the pickup's electrodynamics: the inductance becomes bigger, as a result the resonance frequency is lowered. Also, Alnico is an electrical conductor; this will "drain away" some of the resonance.
All these effects together cause Alnico pickups to sound somewhat warmer, gentler than ceramic-magnet pickups; however other factors such as winding number are of cause also important – it's not really possible to say "that's an Alnico sound".