MM Material Code "Numeric or Alphanumeric"

Dear Experts,

I'm new to SAP MM and was earlier working on Oracle ERP. As a team member, it's entrusted upon me to decide whether the material coding has to be numeric or alphanumeric. Client is insisting on "Alphanumeric" where as I perfer "Numeric" coding methodology.

You all, out of your experience with SAP and the issues related with numeric and alphanumeric system, kindly list out the PROs & CONs of both the systems. Also indicate your preference out of the both options.

Enjoy SAP

Sangmesh