Low-temperature photoluminescence (PL) was used to optimize the structural and optical quality of 2-15 nm thick GaAs/AlGaAs quantum wells (QWs). GaAs wafers, misoriented off (100) towards < I I I >A and < I I I > B were used, covering the 0-0.6degrees misorientation range in steps of 0.1degrees. A dramatic reduction in the 10 K PL linewidth is observed for all 0.2-0.3degrees misorientations, as compared to nominally oriented wafers: on 2, 5 and 15 nm thick QWs, linewidths fall from 23, 8 and 3 meV to 6, 3 and 2.5 meV, respectively, among the narrowest reported to date for similar structures. Above 0.3degrees misorientation, the emission broadens to become, at 0.6degrees, comparable or worse than for the exact (10 0) samples. The 4 K electron mobility of two-dimensional electron gases grown on similar, misoriented substrates increases steadily and then decreases again at larger misorientations. (C) 2004 Published by Elsevier B.V.