Differential received signal strength indicator (DRSSI), in which two separate received signal strength indicator (RSSI) measurements are used to localize an radio frequency (RF) source with unknown transmitted power, has been proposed to eliminate the need for estimating the strength of the transmitted signal in localization. In this paper, the problem of choosing the best pair of measurements, which can lead to close-to-minimum localization error based on Cramer–Rao lower bound (CRLB) analysis, is addressed. The analysis shows that the root mean squared error (RMSE) of localization decreases monotonically with the increase of the angle between two pairing measurements, with respect to the target, up to 180 deg. In other words, it is shown that the best pair of measurements consists of the measurement points which are inline with the target opposing each other. The second best pairing angle is near 135 deg with respect to the target. To practically show the importance of this analysis, several Monte Carlo simulation scenarios were conducted which show that the RMSE of localization would be close-to-minimum using the proposed analysis.