Interesting discussion. Ben Lawry will tell you that straight is the way to go. He did a demonstration for us that made complete sense to me. It was very technical, and I need to do more work to figure it all out for myself, but the conclusion I came to was that he is right for the stroke he is doing. He is teaching a power stroke, similar to a racing stroke, with a very high angle. As I work more on this technique I may find that the bent shaft I've been using for 5 years needs to be replaced, but I suspect not.
I find every stroke and brace easier with a bent shaft because I always know exactly where my blades are. Unlike other commenters, I find myself able to put my hands wherever I want on the shaft for specific strokes or to counter wind. I roll better as well. I can feather it in 15 degree increments if I want, but generally it seems paddling instructors and long time paddlers are moving away from high degree feather paddling because the repetitive rotation at the wrist leads to repetitive use injuries, which I have experienced. Ben Lawry also did a demo to show how a feather makes no real difference in a headwind.
My arms sighed with relief when I got my first crankshaft, and my wrists and hands are sore/numb for days if I use my straight shaft spare for a long paddle.
My final note is that a crankshaft is more expensive than a straight one, but not prohibitively. Good paddles are expensive either way.