With the majority of the teams I ride with we play 1,2,3. Typically 1 is first in herd, 2 is at herd looking for their cow, and 3 turns back for 1 as they pull their cow. As 1 is coming out 2 is already going in. 3 turns back for 2. 1 drops cow as soon as it is committed to going toward pen and will immediately be back at herd to take over 3's position. As 2 comes out with cow, 3 is already heading in. As 3 comes out all riders head for pen together, taking the third cow, closest to hole side takes hole, closest to wing takes that and rider on outside will sweep cattle into pen as a group.
If it is a quiet herd of cattle we may have two or three riders go in at the same time, either splitting herd left right or left right center for safety.
This is what I have been taught by some of the top penners from Canada and USA.