Of course face-to-face is more effective because each person can easily size each up like two cocks about to get into a cock fight. You can't always know the other person's intent in the written word, over the phone, or in other forms of communications.
"The power of face to face communication is more effective than the other mode of communication ?"
Which "other mode"? Face to rear, face to feet, rear to rear? :-/
Really, the mode that's most effective depends on the situation, the kind of communication and desired results. Detailed instructions - best written. Persuasion - person to person. Information gathering - take your pick.
There is no one best or most effective means. That's why we have options.