The particular fly line you have on your switch rod or trout spey rod will impact its abilities a great deal. Some lines are great for shooting sink tips and streamers while other lines are best for indicator fishing or even dry fly fishing. Some lines are good for all around utility work. The other decision that you need to make is whether you want a modular system where the running line and shooting head attach with a loop to loop connection, or if you prefer a contiguous one piece line where they are attached.
There are pros and cons to each line. The one piece lines allow you to fish and cast a variety of distances and there is no connection knots to slip through the guides if you are casting and strip retrieving your fly. The advantage to the modular system is that you generally get more casting distance with less effort because you can use monofiliment running lines. You can also change the shooting head out and use the same reel/running line for different rods. Decisions decisions. Browse these lines and please feel free to email firstname.lastname@example.org with any questions that you might have.