I suspect that the best information on these questions is gained through trial and error by individual pipe smokers to attain their own taste and satisfaction in these matters. I tend not to designate pipes, which with many pipes seems to work out fine for me. I don't smoke Lakeland aromatics with the strong rose-geranium scent, for which I would designate a cob. I also find that broad bowls do better with blends with lots of different tobaccos. As someone pointed out earlier in this thread, that allows more constituent tobaccos to burn at once. As to whether different size and/or shape bowls (cylindrical versus conical chambers etc.) do better with different genres, I think you have to decide for yourself and your own tastes.