When fishing for steelhead in small enviroments, like creeks, they can be really line shy. Clear waters are your enemy! Floro is used because the same pound test is much thinner than it's mono equivalent, making it harder for the fish to see. In clear waters, I'll use a 4 pound leader....at night or stained waters, I'll go with 6 pound.
That being said, all floros are not created equally. I used Vanish last year and had a lot of break offs, but didn't have anything to base an opinion. I changed to Drennan this year and I LOVE it. Bly uses both Drennan and Raven and has been happy with them.