I have tried the Cortland,the SA,and the Airflow systems over the last year and have definately made up my mind on what I do and don't like about each.
The SA is a great line but the loops suck.They are too hard and sometimes stick in the guides.Not good.
The Airflow is the highest floating,slickest and best casting line I tried but my 8wt lines had constant loop and mainline failures last year so I have stoped using the Airflow on anything over a 6wt.The problem is that the welded loops that cast so well,are considerably weaker than all of the other companies' loop systems.Airflow told me that all of the heavy line weights have the same breaking strength as the light line weights and the loops are between 18 and 24lbs(I recieved 3 different emails with 3 different answers to my question regarding their breaking strength).Here in BC,most tackle shops recommend kevlar loops of 50lbs strength and I found out that the airflow loops just didn't hold up well on big fish in rivers.I also found that the mono loop didn't handle the heavy custom heads that I had either.Casting a 350 grain head on this line ended up causing the loop to fail.I had nothing but problems regarding both loop and main line breakages last year on my trip to the Skeena.The info I received from Airflow didn't make me too confident on the replacement lines either so I traded them in for a line that I feel is superior for big fish situations and will allow me to use my heavy heads without fear of them breaking the loops.I still like the Airflow lines in the light line weights though as they are great casting,float high and don't hinge.
The line I traded my Airflow 8wts for are the Cortland lines.While they are not as slick as the Airflow,they come standard with large flexible loops made from 50lbs Spectra.These lines enable me to use whaever heads I want without fear of breakage.They are VERY strong and don't hinge even though they look like they would.I realy like these lines for river fishing and big fish.If you get a snag,it will not break the way the Airflow will(at least mine did).These lines are the ones I would recommend for heavy duty use,unless of course you want to do what most flyshops up here recommend and that is to simply replace the loops on your factory lines with 50lbs kevlar loops.I would do this with any of the other lines on the market,but the Cortland is the only line that comes standard with 50lbs loops.
I haven't tried the Orvis so I can't comment on them.Ihaven't really heard anything about them either.
Lastly,while I haven't tried the RIO,I have heard nothing but good things about them so if I was to recommend one to someone then that would be the first choice.EVERYONE I know who has tried the RIO likes them,while the Airflow,SA,and Cortland will have their followers and their oposers.
Personally I like the Airflow for line weights up to 6wt as it is the best casting line I could ever hope for in a multi-tip,but I don't trust them for heavy usage.I like the Cortland for heavier line weights.It's not as slick,but the line and loops are STRONG.