Can you please tell me which is the best elective subject for doing Bcom ? iam interested in doing cima with Bcom. is cima a tough course?

Can you please tell me which is the best elective subject for doing Bcom ? I am interested in doing cima with Bcom. Is cima a tough course? can you please explain about the merits and demerits of doing cima. I want to go for mba after bcom .So help me please as i have a keen interest for cima.