Out of manual testing and automation testing, which is more effective inidentifying the issues?

In manual testing, the application is tested manually without use of
automation tool. We need to understand when we can use automation testing  and when we can use Manual testing.  

Manual testing is usually done while the software is being developed or any  a new feature is developed and needs to be tested for the first time. Manual  testing helps us in identifying new bugs which may or may not be in  accordance with business flow.  

However, automation testing is done when the Manual testing has been done,
issues have been identified and fixed. We perform manual testing mostly on  stable build and or if some maintenance has been done and we need to perform regression testing.  

Ideally, manual testing helps us in identifying new and variety of bugs whereas
Automation testing is done to perform regression testing most of the time.  The nature of the bugs identified both in Manual/Automation testing is very
different.  

In manual testing you mostly identify new bugs which may or may not directly
impact the business needs of the product. However, bugs identified in  automation has business flow implications. We mostly consider high level  scenarios and automation is 80% times captures the regression need of the product.