Posted 07 May 2017 - 01:18 AM
I think it depends on the circumstances.
Do Medium/CU on the same actor if you're trying to maximize continuity between shots or if you only have the actor for a limited time and need to finish as much of their coverage as possible.
For example, if you have one expensive actor in the cast and need to shoot them out as fast as possible. Or if you have a complicated gag that requires a lot of reset time like blood spatter or wardrobe/makeup changes. It saves time to grab two shots on the shot list at once. This is usually easier for lighting and camera, but worse for sound since they would usually like to get their boom mic closer for a CU, but you will see it in the Medium.
Do opposing shots if you need to capture both actors' performances as they riff off of each other or improvise. Or if there are ego issues with one actor getting their coverage first. Think of the diner scene in 'Heat' with Robert DeNiro and Al Pacino on-screen together for the first time. It makes sense to shoot both angles simultaneously. This is usually more limiting for camera and lighting, but easier on sound (as long as there are multiple boom operators).