For chain link it's hard to beat the Oregon Gator magnum in the biggest size your trimmer will handle. Up to 1.2hp stick with .095 round , from 1.2-1.5 hp you can try .095 square or .105 round or square. Square has a bit more mass and does hold up a bit better. Also try 1/3-1/2 throttle or so to reduce "eating up" so much line. Sure, desert vortex twisted stuff is quieter, and cuts better in good grass. But it doesn't hold up quite as well for edging on concrete and trimming along chain link. I'd also add that the square line seems to be the fungo bat of trimmer line. It slings more rocks for a line drive then round in my experience. And forget about it cutting better. Sure, it does for a second after a fresh trim of the end on the blade of your guard. But in short order it becomes basically round as soon as you use it some. And since most remove the guard on larger trimmers, the end of the line is basically never cut square anyway, thus negating any square edge cutting potential. So basically it just carries more mass than round.
