In your opinion, what is the best method of providing feedback, whether positive or negative, to employees??

In my opinion I would go for the direct approach and would like to add when going through the direct approach it should be communicate to the employees in a very positive way so that, employees would be able to take it positive and would be able to fix the issues according to the requirement of company they work for.

Stand between them  and brief on start of every new day. Start with previous day and usually appreciate them either it was good or not. Don't blame anyone for failure and dont point out anybody. Then tell them about the tasks of going day and importance of teamwork plus communication. Tell your expectations of the day and wish them good day. Small words of appreciation make big difference.  

In my opinion, the very effective method is the direct method to appraise the individual's about his/her positive/ negative aspects. In this method it is easier to convince the individual to improve upon where to focus is to be given more and also, the individuals may express their views directly.

I would take a direct approach, with positive outcome for the employees, s o that they are able to fix their mistakes. If I was the manager of the employee, I would tell him or her waht he or she did wrong, what the consequences are of  their mistakes and how I feel because of these consequences. The tone should by all means be polite. Via this method you'll let the employee understand what and how. For exmaple: You did not work well enough together, because of that your product lacks quality. Because of this I am very dissapointed.

Better to take a certain approach to address issues such as reactions