Arm Positioning for Strongest Stroke

I've been experimenting with arm positioning, trying to find what gives me the strongest stroke with the least fatigue. I've tried everything from the straight arm stroke to an L-shaped stroke, where my fore-arm is perpendicular to the pool bottom and my upper arm is pulling back horizontally, like the arm on an old train wheel. This latter position intrigues me the most and was shown to me by a high-school swim coach. I'm thinking the long arm may be the strongest if the shoulder muscles are built up sufficiently, but I've got to work with what I have. Will keep posting as I find what's working best.