CGI 18lpa Cloud Wintel and Tech Mahindra DevOps Engineer 21lpa offer in pipeline could you please suggest which one better

They will give two months salary compensation if they release you early. 3 months notice period is applicable only if you are in some project. If you are on a high bench period suppose <75 days and crossed bench period limit then no additional notice period,HR can ask you to leave anytime , Compensation will be given in such case.

There is bench process in Tech Mahindra if you are unable to crack internal client interview or find a suitable opportunity for your skill set,There are certain bench period for each band,if you don't find your project within your bench period then company may ask you to resign and leave company.This is a big headache to search project for your allocation within company. If you are aware about the bench process and ok to face it frequently then you can join.This is my experience .