I'm using a 9mm filter unless I absolutely can't. For whatever reason I just get bad reactions to a lot of tobacco, the filters negate a lot of that. Currently I've got a lot of Vauens I love, especially a large Olaf 1811 and a nosewarmer Cut 3152. They just make really solid pipes that never seem to have any issues.
Because of my crippling 9mm addiction I'm constantly checking SmokingPipes.eu for rare 9mm pipes. My dream non-custom pipe is a Peterson Ebony Spigot 107 fitted for 9mm. I've got an unfiltered one, I'm half-tempted to see if it's possible to retroactively drill it for a 9mm but I'm hesitant to ruin a $170 pipe.