Decide whose point of view the scene needs to be in.
Try to chose the character with the most to lose. This will ensure the scene is at its maximum emotional potential.
Sally is going to tell Billy that her four year old son is his, a secret she’s kept since he walked out on her five years ago. Whose point of view do you write the scene in?
Sally has known this information for years, so her anguish is in finally revealing it to Billy and feeling his shock and anger.
Billy, however, is about to be laid a bombshell. The emotional strain will be higher from his point of view, so write the scene from Billy’s viewpoint.
Sometimes people will write a scene from a third party’s point of view for literary reasons. It has a tendency to mute the emotional reactions of the primary characters involved, and sometimes a writer will deliberately want to distance the reader from the emotional scene. This choice of literary device is up to you.
However, for most popular fiction, stronger emotion is usually a better force to drive a scene. This is why it’s best to get into the head of the person who will have the most emotional upheaval in their lives.