Select that one which has maximum correlation. This is equivalent to selecting the point in time where the largest absolute residual occurred. These approaches to developing new variables from model implied series have had outstanding success with time-series data. Unless you deal with anomalies, e.g. unusual values, the estimates of coefficients can be seriously biased. In this example, we illustrate the effect of one unusual value.
Outlier detection requires an estimate of the standard deviation.
This estimate requires the utilization of the predicted value. See for more details on the standard deviation.