Akaike's Information Criterion can be used to determine the 'best' model from a number of alternatives. AIC = N * ln(WSS) + 2 * M where N is the number of data points with non-zero weight, WSS is the weighted sum of squares and M is the number of adjustable parameters. The same weighting scheme should be used for both models (AIC calculations). Ref: Yamaoka, K., et al., J. Pkin. Biopharm., , 165-175