Which is a better B-school, SPJIMR Mumbai or IIM Kolkata?

It is subjective because it depends on many factors like your goals, preferences, and any other individual constraints you might have. It is hard to compare as both are among the top B-schools in India but below is a table comparing the two in different aspects;

IIM Calcutta has slightly higher tuition costs than SPJIMR Mumbai. Different courses are offered by each business school, and IIMC offers more options than SPJIMR Mumbai. 

Although IIM Calcutta has a little higher median income than SPJIMR Mumbai, both institutions' average salaries are on par with those of the top IIMs. While the batch size of IIM Kolkata is not shown in the search results, SPJIMR Mumbai has a comparatively modest batch size.