What color are you using? I find yellow, chartreuse, and white to be much easier to see against the water in most conditions when compared to reds and oranges. Also, opaque colors shows up better. Some slighter materials are too translucent IMO.
I also leave 1" tags on all my slighter knots. They add a degree of visibility of and make it easier to see subtle movement in your slighter.
Right now, I'm using the Cortland stuff but I've had good luck with Umpqua also.
Amnesia is probably my least favorite for the translucency issues I mentioned.