Who is more suitable for the Project Manager role, a Civil Engineer with management skills or a Prof. Manager with Civil Engineer skills? and why?

There is not all-inclusive advise for every case of life, as people are different, and project environment too. 

If listening to experience, I would prefer a Civil Engineer with Project Management knowledge for small and medium size projects.

However, for large scale projects I would prefer a professional Project Manager. If he also possesses the Civil engineering skill, it will be very good advance.

Manager of big project will have a civil engineering team at his disposal, who will solve all construction problems. But solving all the management problem of huge project requires professional problem-solver. He will not even have enough time to delve the technical nuances.

I repeat, the above is just summary of personal experience, not Absolute Truth. History knows examples of professional civil engineers, who successfully managed large projects.

A project manager has to tackle all the knowledge areas (as described by PMI) during the initiation, Planning, execution, monitoring/control and closing. Therefore a Civil Engineer of specific experience would be more suitable for the construction/execution whereas a professional manager with Civil Engineering skills who can manage all the knowledge areas (at least with respect to Planning & monitoring/control especially) would be more suitable for the project manager in my opinion.

for sure the prof. manager would be better and even his knowledge as civil eng. would be an advantage because

1 the skills required by the job as project manager,,,are already available ,,,since he is prof. project manager

2- the knowledge of civil engineering should be an advantage which will help him in some feilds of practice such as team management and quality management