That's an interesting topic dixieman.
I recently interviewed Gordon Smith of FGT Enterprises & Edward’s Pipe & Tobacco in Tampa FL.
I asked him, "what’s the ratio of bent pipes versus straight pipes that you sell?"
He said; "Definitely more bent. It’s probably seven bent out of a dozen. Out of a dozen mix, we’ll sell seven bent today."
That would be almost a 60/40 ratio of bent to straight. (58/42 to be exact).
Personally, when buying a pipe or picking one from the rack to smoke, I don't think about whether the stem is straight or bent. I just reviewed my collection and my ratio of bent to straight is almost 60/40. It is 63/37. I have 10 bent and 6 straight.
I only counted straight as completely 100% straight stems. Some of the bents are very bent, and some of them have just the ever slightest bend to them, but they got counted as bents too.
As far as mouth feel or holding the pipe in my teeth without hand support, I find no difference between bents and straights.
However, a very big pipe, of which I only have one, can be hard to hold with only your teeth.
The one in this picture I cannot really hold in my teeth like that for more than a few seconds just to snap the picture. It is too heavy and I had to support it with my hand while smoking.