I have smoked with most kinds of filters but haven't used them on any regular basis, since I smoke moderately and find they mute flavor to some degree. But my experience makes me think that 9 mm filters are probably the best in terms of actually filtering the smoke, as opposed to reducing moisture.
Also, the idea that 9 mm filters are popular in Europe where tastes for food are cultivated and sophisticated, and there appear to be more pipe smokers per capita, makes me think that they probably interfere with taste the least.
I do notice that most pipes designed to take filter of various kinds smoke just as well without them.
Savinelli balsa filters, Grabow and Medico 6 mm paper filters, and my one stinger pipe seem to smoke well enough with their filters, but the taste is always better with none. If I persisted smoking with a filter, I might only smoke more.