Flat sided cranks have more side-to-side resistance and a tighter wobble, while rounded cranks tend to have less side resistance, so wider wobble. There are various ways to round a body. Through experience, I've found that is is almost impossible for me to round over a bait all by eye and get it symmetrical, especially in a wood that has any visible grain structure. And symmetry is critical. Some guys do a top template to guide how the bait will be tapered. Then they cut facets at the corners of the square blank to make it octagonal, then round those over to a cylinder cross-section. That's basically what I do. In the long run, it's worth going to the trouble to do templates and mark your cuts. Even with the marks, you still have to eyeball it to feather out the facet cuts in the nose and tail of the bait.