Which do you think is more important in project management, academic knowledge or practical experience? And why?

1-young engineer with PMP certificate.

However, I would keep an eye on him.

Because long time ago I was a young graduate with no experience, and thanks to education I got to success in my first job. 

And years later I often use the knowledge sitting in my head since university.

I started studying PM as a separate subject6-7 years ago. And I was shocked, how many mistakes I had made in previous projects, which might be avoided would I have the PM knowledge before.

If you want to keep the company running definitely you are going to find some one with experience in what you do, but if you are looking for improvement and development of your business you need someone with knowledge& certificate.

BTW is there is a young engineer hold PMP? its not applicable

the PMBOK& exam is designed for practitioners so its really hard for anyone without an experience to know what the heck is going on. 

2-an experienced engineer with no PMP certificate...just long good experience.

First of all, if you have more than five years experience, you will apply PMP certificate. It means you need minimal experience in order to be PMP. However, there are important knowledge such as negotiation, human resources, scheduling, cost control that is quite imposible to manage without a lot experience.

Practical experience is more important in project management, and academic knowledge is just an additional. Hands-on people has an edge when dealing with actual problems and issues pertaining to project management.

Practical experience combined with academic knowledge but predominantly practical experience. Because it is the experience that gives confidence to deal with tricky situations and unfavorable conditions.

In my opinion practical experience important because any project has it's complications especially in paper work and unexpected issues. Also it very important in study period as it could estimate the expected problem and timing. 

My thought on the matter. In as much as practical experience is key in project management, academic knowledge can not be overlook. There are always new improve knowledge that are documented, which are shared via academic study.

As someone rightly said, they go hand-in-hand in project management.

It is always best to work on obtaining experience in regards to Project Management, whilst you are continuing with obtaining the qualification. I have also found that its best to create or setup your workplace as a project, that way it assists in putting into the learning into play as you go along.

practical experience because the people that have the exprience are more knowledgable

In project management shall be academic Knowledge, practical Experience, skills and leadership. according ISO 9001 Parrag 6.2.1.  Beside Work ethics and honesty.

I think both are important matter. Practical + theoretical = Complete project knowledge.