Anything you enjoy. I think being selective about which blend refers to getting a nice even carbon coating going, so for that purpose you might want loose tobacco in a finer, more even cut, as is true with most codger blends and many other burley and Virginia blends. Break-in also relates to cake-building, and I am one of the minority who doesn't think cake helps either the pipe nor the smoking experience. I wipe the pipe bowl out after each smoke and want only to maintain a thin carbon coat. No reaming, ever. Some of my pipes, bought new, and now nearly forty years old, still smoke great. But many like this cake idea a lot, so, your call.