Re: closed back v. open back
Ceramics are punchier and don't breakup as soon, which compliment the closed back design - which is very direct like STRATDELUXER97 mentioned. Alnico speakers are usually warmer with more compression/creamier which compliments the more open dispersion of sound of the open back design.
As a disclaimer, I'm stating this as a "general" assessment. There are higher power handling alnico speakers as well as lower power handling speakers that are ceramic, it's all a matter of specifications from the manufacturer.