I don't find a great deal of difference in taste between meerschaum and charcoal filters. The meerschaum are more effective at absorbing moisture, but since I only smoke bent pipes as they're more comfortable for clenching, I don't really get moisture problems.
My preferred filters are Vauen Dr Pearl charcoal. The White Elephant are good but they're fractionally larger than the Dr Pearl. No problem 99% of the time but I've got a couple of pipes in which they're a bit snug and if they do swell with moisture they can become restrictive.
Also, with WE charcoal I sometimes find a granule of charcoal gets through and ends up in my mouth. I've found this to be much worse with Savinelli filters, to the point it gets annoying and I'm splitting them out. Less of a problem with WE. Never happens with Dr Pearl.
Thank you for your reply and for the tip regarding troublesome charcoal granules -- different brands of filters do feature different number/size/shape air holes at each end.
Variation in 9mm filter width is an interesting topic. I have identified three variations, from wide to narrow:
white elephant, everybody else, and Dr. Pearl.
Dr. Pearl, being narrowest, will fit any 9mm filter pipe, but I don't like how the filter moves back&forth in pipes other than Vauen, so I wrap some scotch tape around the filter, so that it fits snug, and prevents smoke from slipping around the filter.
On the other extreme, white elephant filters are too wide for my Vauens, and my Chacom!