Which of the following trait is most important for a project manager? 1)Communication, 2)Team building, 3)Technical expertise, 4)Project control?

Communication, without it you can not make a team building, and can not take any corrective action.

I think all the aspects mentioned in the above question are important, and we cannot survive if any of the quality is missing.

i think Team leadin is most imfortant. and also Communication have more valuable. because coduld't any work  without proper commounication. 

Communication and team building goes hand in hand, effective communication always makes the job of team building easier. Then comes the Technical expertise and with an effecrtive team building process, Project control will be a much easier job. Every aspect is inter-related, except for its sequence of aplication may change from person to person, as a project manager.

I would rank them in the following order: Communication, Team Building, Project Control, and then Technical Expertise.

it's impossible to build a project without any of this4 basics

for the beguining you build a team with a requested technical expertise and should communicate with them and to them  to control your project. its very related points for the succes of any project

Communication is the most important for every Project Manager. There are many online Communication tools that can help you to manage internal and external communications. They include:

- Tools used for direct communication - E-mail and online voice and text chat

- Collaboration Tools for Sharing documents and working Remotely

- Social media Tools for internal communications and announcements.

5 Following things should be considered while going for Online Communication Tools.

Connectivity and Security

Redundancy

Standardization

Disaster Recovery

Growth

Best Team Communication Tools that can be used at Work

http://Slack.com

http://Grouprocket.net

http://Hipchat.com 

I suggest "communication".

I would say Communication plays a vital role as it covers80% of the Project Management. Then we could consider Team Building, Technical Expertise and Project Control. If this sequence is maintained, then hopefully things will be pretty in control which even incorporates the quality of deliverable(s) achieved.

All of the mentioned items are important for a project manager with different priority we can put

them as follows according to their importance

Project control

Team building

Communication

Technical skills