Hi.

Each and every exam for job prospectus or graduation is difficult. Depending on your interest and the career you wish to pursue. If you wish to go in Civil Services then UPSC, if you wish to be in research and sciences then ISRO Exam is the way to go, AFCAT is for  Commissioned Officers in Flying, Ground Duty (Technical) and Ground Duty (Non-Technical) branches.

These all are somewhat mutually exclusive, that means if you prepare for one you might not have enough time or interest for the other. Incase you have a specific query about one of these exams. Please feel free to comment.

Best of Luck