dear student

For production engineering students they should prefer PI because all things they learn in four years of degree are asked in PI paper.

The students who are very interested in design can give from mechanical(ME). If you are giving from mechanical then you have to do lot of hard work for it. You have to study all the design part which is not usually covered in production syllabus.

You can get into IIT's from both the streams. You will have to select specialisation according to the paper.

If you are giving from PI then you can go for

Industrial engineering

Operation research

Manufacturing etc.

If you are giving from ME then you can go for

Design

Thermal

Automobile etc.

hope this helps

All the best!!!