I agree with those that say Inkscape, it's where I've designed all my logos. However, I've been tempted to try using FreeCAD to do it lately. I'm not sure if it can export as SVG, but the thought of have a proper parametric tool for designing logos sounds up my ally. I tend to try to treat Inkscape like one, by liberal use of construction lines, but at the end of the day, it really doesn't like being that precise.