Which is the best Test series available for non CAT exams? Particularly NMAT, IIFT and SNAP.

The test series conducted by TIME is the best for CAT and non CAT exams like SNAP. 

For SNAP there are various test series available on testfunda conducted by scmhrd and other symbiosis schools. 

These mock tests will give you better ideas of the exam. Also, Map the SNAP book by Arihant has past 10 years questions of SNAP and you can refer to those.

You can also go for Gradeup. It provides the best test series available for all MBA entrance exams. These are prepared by expert faculty with a lot of experience, they also provide you with complete analysis and detailed performance reports to help you improve in the right areas.