I prefer the sound of NOS designs because they sound more natural to me. I'm an amateur classical guitarist and dabbled in playing the piano and sax when I was younger. Vocals, piano, guitar, sax in particular sounds more like the real thing on NOS filterless design. However, NOS does tend to dampen the HF. OS designs have more "sparkle" and more spacious sound, but they don't have the body and truthfulness of instrumental timbre of a good NOS filterless design. But I haven't heard the ultra expensive stuff from Esoteric, Burmester, etc. in a familiar setup.
