which is best part time post graduation course for me?

i have passed b.com before 4 years, and i have been working in power supply company as office assistant in complaints department, I thinking to do any course. which post graduation course(part time) should i do on base of b.com and my work experience, If i go for mba, which specialisation should i choose?
finance, HR, customer care, or other among these whis mba is suitable for me?
If any other course suitable for me…..