It is tough to choose between SIBM Pune and IIM Shillong. SIBM is quite an older institute and also a reputed one. It was founded in the year 1978. It has a good placement report. The average package offered at SIBM Pune is 21 lac per annum.
IIM Shillong, on the other hand, is a dream B-School for many. First of all, it is an IIM. The name will be going to remain with you for the entire of your life. IIM Shillong also offers excellent placements. The average placement at IIM Shillong is 22 lac per annum, and the highest salary offered is 55 lac per annum.
If I had both options, then I would have gone for IIM Shillong. The first reason is the IIM tag, and the other is that Shillong is the best place to spend two years of my life.