You could change the default number of sides used to create the circle in the first place. The default value is 24 but you can set it higher. Perhaps you would get a smooth enough curve at 60 or 120 sides although you can go higher. Keep in mind that this will increase the file size possibly very dramatically. Don't increase the number of sides unless you need to. You do have to make the decision on the number of sides before you make the cylinder or otherwise extrude the curve.