MAT

Here is a list of exams in the increasing order of their difficulty:
ATMA (the easiest, gave once, many of the questions were wrong. Very poor standard of the exam. Score 98+%ile).
MAT (I personally felt that the May 2017 exam was a few notches easier than the September 2017 version of the same. Scored 99+%ile).
CMAT (did not give it till now, but from what I've heard, this is another speed test, so questions are easier. Tad above in difficulty level from MAT).
NMAT (another speed based exam, will appear in October this year. Although there are no negative marks, one must score 215+ out of 360 for a sure shot convert into the prestigious NMIMS).
SNAP (harder than NMAT though the difficulty level is almost same as that of NMAT. Harder on the list because of the GK section as well as negative marking).
CAT (will appear this year, no need to tell why this is at the bottom where the most the toughest reside).
XAT (a stick higher than CAT, XAT is perhaps the most difficult when it comes to management exams. Partly because of its higher level of Quant and LRDI and partly because of its decision-making section).