These days, it is the rare individual who does not bring a lasting ambition to cast a long line when he first picks up a fly rod. As a tool designed specifically for this purpose, a weight forward line is generally the first choice of a beginner, and many will never try anything different.
Like anyone else, I appreciate the ease in which a weight forward taper can be applied in situations where a long, straight line cast is the foremost objective. This especially applies to still water fishing where a floating line is not subject to the same factors found on moving water.
With a lifelong fondness for fishing dry flies on the predominantly larger rivers of the Rocky Mountain west, my preference lies in a much different line configuration when compared to the popular weight forward taper.
On moving water, inducing a natural presentation of an artificial is often almost equally dependent upon casting and mending. With maximum control both in the air and on the water as requirements more important than easily attained distance, my choice is a double taper floating line.
Even on big waters, I try to wade within 30 feet of a feeding trout. At this range and anything less, the performance of a weight forward and double taper line are essentially equal. It is beyond this distance that I begin to struggle with line control when fishing a weight forward taper.
Unlike a weight forward, there is no hinge point with a double taper because the weight of the line is distributed throughout its length rather than being concentrated in the first 30 feet. With consistent flex and contact with the rod tip, a double taper permits superior line control while also making it easier to regulate the velocity of fly delivery. And while there are exceptions, shooting slack line into the cast is not something I generally apply when presenting a dry fly. Additionally, I find it difficult if not impossible to make certain casts that rely on controlled line speed or consistent response to the rod tip when fishing a weight forward beyond 30 feet. Curve casting, aerial mending, and a long reach cast are much more easily accomplished with a double taper.
Precise mending techniques are vital to managing the drift once the fly is on the water. With the thinner running line in the guides, it is virtually impossible to reposition the heavier front portion of a weight forward taper as a means of overcoming problematic currents that can disrupt a natural drift by causing the fly to drag.
Refined nymphing methods involving submerged flies in moving water can require precise casting and deft mending techniques that are quite similar to fishing a floating imitation. Whether maintaining a natural drift or inducing controlled action to the fly, it is not unusual to experience some difficulty when fishing beyond 30 feet with a weight forward line. For the same reasons that apply to dry fly fishing, I generally prefer a double taper when presenting a subsurface pattern to a big, nymphing trout in moving water.
In keeping with the example of old time steel-headers prior to the popularity of two handed fly casting, I rely on a double taper floating line for spring and fall streamer fishing for trout when the water is low and often quite cold.
Swimming the fly mostly with the current or on a slow, pulsating swing often involves long, looping mends that may require some serious roll casting to execute correctly. And while a long cast on big water may require significantly more effort, I find 60-70 feet to be a reasonable distance for a 6 or 7 wt. double taper. Again, as in other situations discussed herein, I value line control above ease in gaining distance for low water streamer fishing where presenting the fly means considerably more than simply stripping it quickly through the water.
I have many highly accomplished friends and acquaintances who will stick with a weight forward line for virtually all of their trout fishing, and many will disagree with my comments and personal opinion regarding a double taper. This I accept without argument because fly tackle performance is an entirely individual matter, and I would never try to convince anyone that my way is best.
In general, I believe a double taper to be a specialized line best suited for refined presentation of dry flies on moving water. But failing to understand its versatility is a common oversight by many who might benefit by simply giving it a try.