What is the better option for an undergraduate course from PEC University Chandigarh, mechanical or aerospace?

It all depends on your personal preferences and what appeals to you the most. However, if none of these two branches piques your attention, then definitely mechanical engineering in PEC is the way to go. 

• Mechanical is often favored over Aerospace in terms of placement, faculty, or any other criterion.

• Mechanical is an evergreen branch, as they claim, and they call it that for a reason. 
• It is in high demand. All industries will need the mind of a mechanical engineer today and forever.

It would be advised that mechanical is always a better choice than aerospace. You can choose to go for Mechanical engineering without giving it much thought and discussion.