For me, it's somewhat random. I make it a point to have "favorite" pipes in the line-ups for all the different types of blends I smoke -- English, Balkan, straight Virginias, VA/burley flakes, Lakelands, and aromatics. My favorite favorite pipes, though, are all dedicated to a single blend: Penzance. And my least expensive pipes are all dedicated to Lakelands and aromatics. My one meerschaum is primarily a Lakeland pipe.
I know right now, though, that the next pipe I get will definitely be a Lakeland pipe, regardless of what it is. I've discovered a couple of Lakeland blends that I just love, and the three Lakeland pipes I have now just aren't enough to handle the frequency with which I'm smoking them.
I will add that I do tend to have oil-cured pipes dedicated to straight Virginias; for me, the oil-curing process really helps straight Virginias to shine.
Bob