Box-Cox MLE lambda=0.468 is the paper's central result; they present KWH^(1/2) because lambda is not significantly different from 0.5 and elasticities are easiest to interpret in that form, and they quote its -.42 elasticity first. So obs 2158 (KWH^1/2, -0.42) is preferred. || 'the model best fits the data when the quantity of electricity explained by the demand equation is raised to approximately the one-half power' (p.179); 'the estimated value of lambda is very close to (and not significantly different than) 0.5, and it is somewhat easier to interpret coefficient estimates and calculate demand elasticities when the equation is expressed in this form' (p.188); 'the price elasticity is -.42 ... for KWH^(1/2) as the dependent variable' (p.188).
Munley, V. G., L. W. Taylor, and J. P. Formby (1990): "Electricity Demand in Multi-Family, Renter-Occupied Residences." Southern Economic Journal 57(1), 178-94