In general, I have found that the New Japan Radio versions (the NJM parts) are very high quality and show low measured distortion compared to other varieties. I have not done these tests in a long while, but back when I did, using an AP2322 analyzer, I seem to recall that low order distortion was lower in level with the NJR parts, and high order harmonics, which I think are probably more important, were also lower in level. In general, New Japan Radio seems to have very good process control, and makes very high quality versions of the standard devices.