For most situations I prefer the ceramic one. Its still thick and mean, but has a tighter bottom end and improved clarity for high-gain applications. I love the Warpig in brighter guitars, such as maple neck-thru ESP/Jackson styles as well as bolt-on alder/ash guitars. In a Les Paul or a PRS it also sounds great, albeit warmer. The alnico Warpig I think would be cool if you want a bit of a fatter, looser sound, or perhaps to tame extremely bright guitars.
I have the Warpigs in an ESP Horizon-I and its the best tone ever. I pair it with a Sinner in the neck :)