As a project manager : Do you prefer to hire general engineer who has some knowledge about most items , or hire specialist engineer has all knowledge about specific item . Why?

Depends on what position are you hiring for and the nature of the project you are working on. But I guess in any project there should be both general and specialist engineers for work to be delivered in the right way 

I would proceed purely based on the requirement and work demand. Thanks.

If the economic issues have the priority , I will hire the general engineer because he will take low salary depending on his little knowledge about most items , and his experiment will grow according to his work years but I have to put him under supervising of the specialists if possible.

It Depends on the scope of the project but usually most have a mix of both specialist n general this is so as to have the work delivered in the best time n way possible

As project manager for a big scale project i will hire the specialist engineer and i will make the good coordination  and communication. 

Hire the professional who has the general knowledge for most of the items if numbers of specialties are more or in case the projects required specialists only for few items, then hire one general and one specialized  in that field of requirement so that he can guide the others too.

In common, project team should comprising both general and specialist engineer.  If the project is already having the Core team (Core team means the subject matter expert engineer/s) then you can hire general engineer and train/mentor them by expert engineer.

It depends on your situational requirement, Case 1: if your need is for particularly a specific category then going for hiring a specialist engineer who has specialization in that subject is the best option rather than choosing an engineer who has some knowledge in all items because you don't need to train him on the subject Case 2: If there is a team support to manage the requirement and the requirement is not particularly related to a specific specialization then choosing the general engineer with some of the knowledge in most of the categories is good than selecting a only specific specialized engineer.

Actually Projects are divided into phases. I will discuss three only.

Initiation / Planning:

In this phase project details are developed. Project management plans are developed. Major technical details are developed. In this phase Project Manager (PM) may require expert opinion at several stages. So Expert and Specialized Engineer / professional have their own role and cannot be avoided, specially if the project is complex in nature. However fresh engineer have their own role and may be given the task to innovate the things and be a part of project for better involvement in upcoming phases.

Initiation / Planning:

In this phase all works are carried out according to developed details and project management plan. So one may depute Engineers with less experience to follow and implement details mentioned in plans. So one will require engineers for implementation only.

Further one may also outsource the jobs of either fresh engineers or specialized engineer according to nature of project. All you have to do is risk analysis.

Monitoring / Controlling:

In this phase (it runs parallel with execution) you may depute Engineers with less experience. PM develop check list, engineers fill them being on site. These duly filled checklist are analysed either by PM or Specialized engineer to gauge project progress or apply control measures.

 

So in Project Management their is no hard line for your question. It is just the game to search for options and analyze them in the light of your project, governing laws, availability of resource and definitely cost of resource.

It is good to have3:1 ratio of both type. If we have3 General Engineers and1 Expert Engineer, it is good in terms of company budget as well as growth of company as well as individuals. One Expert Engineer can train the rest of the3 General Engineers. Tomorrow we have hired within the budget and additionally produced3 additional Expert Engineers for the company.  And yes this logic is again depending on the nature of the project and the selection process. 

You only should hire what you need.

If your requirement is for one source for bits of this and that, then you need a general engineer. If you're requirement more into high technicalities in a specific area, you are obliged to a specialist.

What is most important is actually what do you need?