Hey mate,
I have one of each magnet in both my Les Paul's, one is in drop c tuning (ceramic) and one flits between standard/drop d/c#/c (alnico).
The differences I notice is the alnico is very thuddy and bass heavy, with lots of punch. The ceramic is more mid range focused and cos I'm in a lower tuning it works well in my mahogany guitar. For drop B maybe go ceramic?
What guitar have you got?