Whigh is best ?
Architecture or machanical engineering
Both Architecture & Engineering are great fields to be in. However, your choice must not depend on the opportunities once you graduate. Rather, your choice must be based on your personality and fit with the program.
Engineering is more suitable to Left Brain dominant individuals - or those who have an affinity for numbers, logic etc. Engineering entrance exams like JEE Paper 1 & JEE Advanced will test you primarily for these skills.
Architecture requires both Left Brain and Right brain skills sets - i.e. Logic / Analytical as well as emotional / creative skill sets. Hence, entrance exams like NATA & JEE Paper 2 will test you for both logical / Analytical skills along with Creative skills like spatial ability and Design sketching.
Try taking this Aptitude Test - It will probably help you understand your skills to make a good decision