In three-dimensional acoustic source localization, setting the steering vector is an important choice. Four steering vector formulations are frequently used. In the noiseless case, two of them yield a correct estimation of the position, the two others yielding correct estimation of the amplitude of the source, assuming its position is known. Here, noisy measurements are considered, and the steering vector formulations are compared in terms of bias and variance of the estimated position and amplitude, allowing a more informative assessment of their performances. An approximated value of the position bias of the biased formulations is given. Maximum likelihood estimation of the parameters of the source is derived, showing that it involves the combination of two steering vector formulations, for position estimation, followed by amplitude estimation. This analysis does not rely on the specific form of the Green function, and remains relevant for general propagation media.