While both are amongst the best B-schools in India, SP Jain takes the course due to the relatively lower batch strength of 250 compared to 600 at NMIMS which is very high when talking about MBA students. In terms of academics and infrastructure, both SP Jain and NMIMS cancel each other out. Placements too are excellent at both campuses. If a choice had to be made, I'd choose SP Jain simply because of lower batch strength.
Another factor to consider is the affordability. SP Jain charges around 16 Lacs for tuition and accommodation while NMIMS charges around 11 Lacs. If money is a major factor you're considering for choosing an MBA college, NMIMS is a much better choice.