I am a fan of the 2 - 2 - 2 but, I will deviate from that when the time calls for it. Using this as a general practice, is a good idea though. You can expect your enemy to be doing something similar in most cases. Sometimes I will throw an attack in there for defense once the first point is lost. I will use that character to break up their lines as they try to regroup. This will also distract them from the objective. It can be more effective than grouping up at times.
Dive Comp - Kings Row
Winston - Genji - Zarya - Zenyatta - Lucio - Tracer
This is a little dated but it breaks down the team comp process pretty well.