Like to do SAP course pls suggest which module is better?

I am from B.sc. computer science background and completed my MBA Marketing in distance mode now i am working in direct marketing from last 5 yrs, now i am interested to do SAP which module is preferable for me to learn basing on my experience SAP MM or SD i am very much interested on SAP MM but as per reference saying that SAP MM is use ful for those who done their B tech on mechanical electrical it is better for them SD is useful for Marketing people. Please clarify my doubt...