I have used most of the brands of string as I would get a chunk as needed from the crews and I got whatever they had. 2 tricks make a huge difference regardless of brand are to keep the string moist. I store ours in a jar or bucket filled with water.
The more useful tip is to slow down the line if you are up against a hard object like a concrete wall or a fence wire. Just enough throttle to make the string cut. The same applies to cutting the weeds in the gravel area, just enough throttle to cut and not shoot rocks everywhere.