Best functional module to leran for SAP SD consultant

Hi,

I have done MBA .I had 3 years of domain experience in sales and services.When I was in service dept, I was familiar with ware housing activities. After that I moved to SAP, and I am certified SAP SD consultant.I have been working as a SAP SD consultant for the last three years.Now I want to learn other module. In My current project I deal with SAP SD and part of warranty module.I am totally confused which module to learn .I am unable to pick among SAP WM,SAP MM, SAP CS, SAP CRM and SAP GTS. what is best module for SAP SD consultants to learn and what are the the career opportunities ? I have searched in Google, I have came across so many posts regarding ABAP and functioanl module. Please advise and correct me If I am going in wrong direction.Appreciate your help and sincere advice.

Regards,

Suresh