Head and shoulders the 2 best light lines I've used are Gamma and Sufix Promix. Strong, low stretch, scratch resistant, very limp, and they seems to last forever so you don't have to respool 3 times a year.
I'm going to add a bit to this post. Take a fresh section of either of these lines in 6lb test and try to break it with your bare hands and unless you have bricks for hands your likely to hurt yourself. These are tough, thin lines. Any other 6lb test is pretty easy to break with your hands. I've done that test with so many people on the road, more times than I can remember, and without exception I get raised eyebrows for an amazing 6lb test line.