Narrower diameter line is INHERENTLY sharper, and you'll get a faster, cleaner cut. I use Sufix Megatwist .095 which is actually narrower than round .080 line. It cuts cleaner, faster, and I can use a smaller-engine, lightweight trimmer (Tanaka 230) and still cut a wider path than if I use larger diameter line. A larger diameter line might last a little longer than smaller diameter line. But who cares -- using thinner line you can wind more on a spool anyway, and it takes me no more than 3 minutes to wind a spool with fresh line. And oh yes, I've tried MANY different types of line in different diameters.