Both colleges are worth considering for a good career. Since its establishment in 2006, IIFT Kolkata has been climbing the ladder to success. The excellent performance in corporate competitions is a testimony to that. IIM Shillong is among the fastest-growing new IIMs and its alums are making a name in the industry.
We usually judge a college's worth based on factors like Alumni network, teaching pedagogy, corporate competition wins, etc. Yet, here I am going to simply make a domain-wise comparison. This is because when choosing a college focus should not be on the college but on your own interests. Identifying the domain you want to enter is necessary only then you can choose a college that excels in that respective domain.