Which is more appropriate: completing the first row or filling the gaps by joining another row?

It is best to complete the first row, and it is not permissible for any worshipper to delay from the first row to pray alone behind the row, because that is not legislated and leaves a gap in the row. If a worshipper comes and finds the row complete, he stands alone, and his prayer is valid due to the excuse. As for pulling someone from the row, it is not permissible due to the disturbance it causes, the creation of a gap in the row, the injustice to the pulled person by moving him from a superior place to an inferior one, and the harm to the row by its disruption.