We have measured the absorption, gain and spontaneous emission spectra of GalnNAsSb (3.3%N), GalnNAs (0.5%N) and GalnAs quantum well structures to compare their merits as laser gain media. The parameters describing the relations between peak gain and current provide only limited insight. From the analysis of absorption spectra we have determined the intrinsic properties of the structures, represented by the product [reduced density of states × matrix element × overlap integral], taking account of differences in operating wavelength, well width and confinement. We find only a small variation in this product across the samples. The GalnNAsSb structure has a low radiative recombination current due in part to its low photon energy and also to differences in conduction and valence band densities of states and less inhomogeneous broadening relative to GalnNAs. We speculate that Sb brings benefits as a surfactant producing more homogeneous wells so Sb may also be beneficial in structures at shorter wavelength. However, there is a large non radiative current in GalnNAsSb and achieving further reductions in the non-radiative current is the major challenge in taking advantage of the good gain potential of this system.