Here is a good introductory video on how to select the right fly line for your Switch rod. A Switch rod can be used for either overhead casting or Spey casting. If you want to know more about Switch rod, please refer to my earlier post on Why Switch Rod .
To supplement this video, I am including a more comprehensive guideline below:
Lines suitable for Skagit Spey casting with Switch rod:
1) Wulff Ambush line - wonderful line that cast easy even with minimal D-loop. Available also in intermediate sink as Ambush Clear Head or the slower suspend sink Ambush Neutralizer.
2) RIO Skagit Short - good for turning over very big fly or very heavy sink tip but clunky
3) RIO Skagit Flight - a more refined version of the skagit short. Available in intermediate sink as Skagit iFlight.
4) SA Skagit Extreme - SA version of the Skagit Short but with a more refined front taper but still plenty powerful. Available also in intermediate sink.
5) Airflo Skagit Compact - a favourite of many skagit caster in the early days
6) Airflo Skagit Switch - a shorter version than Skagit Compact more in tune with Switch rod
Lines suitable for Scandi Spey casting with Switch rod:
1) Wulff Ambush line - make sure you match it with a 15ft floating or clear Versileader before attempting Scandi casting with this line or it will prove too short
2) RIO AFS
3) RIO Scandi Short - this line was designed after AFS to cater to shorter Switch rod
4) RIO Switch line - this line has long back taper suitable for mending but not so good for shooting line
5) RIO Steelhead Scandi - designed for rods 13 ft or less. Long 22ft front taper design supposed give better presentation.
6) SA Scandi Extreme - a very long front taper scandi line.
7) Airflo Scandi Compact
Lines suitable for double hand overhead casting with Switch rod:
1) RIO Outbound short - 30ft head. Comes in floating and intermediate sink; tropical or cold water formulation.
2) AIRFLO Forty Plus - 35ft head. Comes in floating and multiple sink version.
3) Wulff Ambush line - This line is so versatile that it can shoot with the best of them. Just match it with a 10ft versileader to form a 30ft head and shoot away.
Lines suitable for indicator nymphing with Switch rod:
1) RIO Switch line - the long back taper ensures easy mending
2) AIRFLO Speydicator - with 12- 15 ft rear taper for good mending.
3) Wulff Ambush line - This line works great for indicator nymphing as well. It will turn over heavy flies easily even in tight quarter.