Apparently I have no one favorite. For classic style, a straight tapered stem is plain and elegant, but everything else has its place, from chair-leg stems, and extreme bends like Oom-Paul, to saddle stem, vertical saddle stems (of which I have only one), and all degrees of bend from slight to U-Turn. I even like orange swirl colored stems on MM cobs, and long churchwarden stems both straight and arched. That variety is why I have way too many pipes (by my standards, not by everyone's).