One of the long standing myths in fly fishing is that a Double Taper (DT) fly lines are more delicate than a Weight Forward (WF) fly lines. In reality, both tapers can be very delicate or very aggressive depending on the design of each specific line. In today's market we can purchase products that are specifically designed for delicate presentation, aggressive presentation or somewhere between. Simply stating that one profile (WF or DT) is more delicate than the other is too broad a statement. To decide if a line is aggressive, delicate or a "tweener" we need to take a close look at the front taper, belly and rear taper. The characteristics of each specific line dictate the delicacy or aggressiveness so we could have a WF or DT that both have delicate delivery at fishing distances.
Luckily you don't have to take my word for it. Bruce Richards provided the following information several years ago about this subject after I pestered him with an email asking for advice on the subject. In case you don't know, Bruce is one of THE guys in fly fishing. Now retired, Bruce resides in Montana after fulfilling an amazing career working for 3M Scientific Anglers. If you've fished an SA line in the past 30 or so years chances are Bruce built the tapers and has forgotten more about each of the lines than I'll ever know. Bruce is an accomplished caster and casting instructor who is heavily involved with the Federation Of Fly Fishers (FFF). http://fedflyfishers.org/Home.aspx
Here is Bruce's take on DT vs. WF:
DT vs. WF Which is REALLY Better
Few fly line subjects have been discussed more than which is the better taper, double taper (DT) or weight forward (WF). The answer is, neither is inherently better, but one may be better than the other for you.
A lot of generalizations are made about these two tapers based on outdated or incorrect information. We've all heard that DT lines are more delicate, give better control, roll cast better, etc. In some cases some of these things are true, but not always.
Delicacy of delivery is determined by the mass of the front part of a fly line. This is determined by line diameter (which relates directly to mass), and taper length. A line with a small diameter tip and a long taper has much less mass up front than a line with a large tip and short taper. Don't be mislead by taper length alone, a line with a long front taper but a large tip diameter will not deliver delicately. A DT and a WF line with the same taper and tip diameter will deliver the same.
For many years most DT and WF lines were made with the same tip diameter and front taper length so there was no difference in how they delivered, although many claimed there was. Today, some of the DT lines are actually designed to be used specifically for spring creek type fishing and do have longer tapers and/or smaller tips.
Anytime a line (or any product for that matter) is designed to do one thing very well it usually has a shortcoming somewhere else. Lines that are designed to be very delicate have little mass in the front to carry larger or heavier flies, and don't handle windy conditions well. It takes a better caster to throw the kind of loops it takes to make these lines perform their best. And no, DT lines aren't more "accurate" at normal fishing distances, that is entirely in the realm of the skill of the caster. Good consistent loops and practice are where accuracy come from.
It is very true that DT lines are easier to control and roll cast at longer distances than WF lines. At shorter distances there is no difference. The key to line control and roll casting is that large diameter line belly must be in the rod tip. If small diameter running line is in the tip it is nearly impossible to transmit enough energy through it to the belly to make the line do what you want. What many people don't consider is that WF lines control and roll cast as well as DT lines at the distances most people fish.
Most WF lines have heads that are 35-40 ft. long. Add a 9 ft. leader and the distance to the fly from the end of the head is 44-49 ft. To that, add the length of the rod since roll cast normally end with the rod parallel to the water and pointed at the target. That is the distance at which DT and WF lines control and roll cast the same. There aren't many typical trout fishing situations that require roll casts longer than that, and not many casters who can roll cast that far. What this all means is that DT and WF lines work pretty much the same at the distances we fish most of the time.
Certainly if someone fishes a big river that requires a lot of long distance roll casting and mending he or she should consider a DT line or a WF with a long head. Rods longer than 9 ft. are almost a necessity also, roll cast distance and mending performance is directly dependent on rod length.
Everybody knows that WF lines are better for distance than DT lines, but is that really true? Well, yes, but the difference isn't as big as you might think. Certainly WF lines shoot better because of their small, light running lines. But remember, this benefit starts at 44-49 ft. when the running line is in the rod. If you will be making a lot of long casts it is certainly a little easier to do with a WF line, but don't think that DT lines won't shoot, they will, just not as far. With the advent of new slick coatings like AST DTs shoot better than ever.
For most people it probably doesn't make a lot of difference which taper they use. Most of us fish at distances less then 44-49 ft. which is where WF's start to shoot better, but lose line control. Most of us don't have the need, or the ability, to roll cast longer than 45 feet.
So, how do you decide which is right for you? If you do mostly small fly fishing at short to medium range there is no reason not to get a DT line. There is always the budget issue, DT lines are essentially 2 in 1 so are less expensive over time. If you are consistently throwing long casts you will be able to make them with fewer false casts with a WF line, but lose the ability to do long roll casts and mends, if you ever need them, and are able. For most of us it doesn't make much difference which taper we use most of the time, make your decision based on how much short distance fishing, or long range fishing you do.
I might add that it is a physical impossibility for a DT to be more delicate than a WF. Assuming the two front tapers are identical both profiles will deliver with the same turnover and delicacy UNTIL you get to the running line on the WF. At this point the WF actually becomes more "delicate" in that it has significantly less mass in the running line portion of the fly line. A DT keeps the same thickness throughout the body of the line until finally tapering down at the opposite end of the line. So, the farther you cast a DT the more mass you get landing on the water thus increasing overall weight making the DT less delicate.
I'm of the opinion that for Trout in moving water you can get the job done with either profile since most fishing is done inside of 40 feet. In lakes or specialty applications a WF often has desirable characteristics which make it the more popular taper design.
Either way, get out and fish your favorite line.