I've had a few filter pipes, ala Dr. Grabow and Savinelli, and I've got to say that I much prefer unfiltered pipes. Actually, when I'm window shopping the internet (or anywhere else for that matter), I'll gaze at a filter pipe, but won't even consider buying it. IMO, putting anything in the airway restricts airflow and ultimately causes a less rewarding smoke.
That being said, if you buy one and just don't use a filter (or their little adapters) you get a wide open draw which makes smoking your pipe quite pleasurable. You just have to be careful and really sip on them.