Use the interpolated spline. The reason why you use a interpolates spline is because you want them smooth, and no jagged edges, if you can help it.
We will have some jagged edges because of turning to low poly, though.
here are a few ways to make easy arms. This tutorial will teach you how to loft them from four profile interpolated splines. Although making a basic arm is easy, making it look detailed and defined is yet another story for another time and tutorial. Here goes...