I went over to using Airflo G3 as it is a finer diameter than the equivalent breaking strains of Fulling Mill line. I feel this is important when fishing in clear water or for dry fly fishing on Commercial fisheries.
In terms of cost while on the face of it, it is priced often as much as twice the price of Fulling Mill in reality many angling stores sell it under BOGOF offers ( Buy One Get One Free) so its not much different if buying two spools.
I have had no problems with the 10lb and 8lb line however I have to say I have had problems with the 4lb and 6lb line.
I had a spool of 4lb that I used a lot in the 2011 season and it was OK. Then I went on a river trip late in the season ( early Grayling season) and was broken off a few times in succession on not huge fish. I then found I could snap the line alarmingly easily. Basically half the spool was wasted as i could not trust it, it seemed to be way to easy to break. I was asked if I had ever had the spool wet and in fact it had been in my vest pocket a couple of weeks before when I got drenched. I was warned this can be a problem and I have to say it seems to be a problem. A new spool I have kept dry has been fine.
I have also had some issues with 6lb where I have had sections of the line on the spool that seem very easily broken. I cannot say I have knowingly had this spool wet but i find if i pull off a few feet and pull test it some sections snap, others are fine. A quality control issue? no idea, but I have stopped using it.
I have had no problems with 8lb or 10lb, it has outlasted some hooks after violent takes so not concerned about this line type.