DT vs. WF ?

When is one better than the other?

They are about the some out to 30-40′, then the WF has a thin running line where the DT stays the same size until the head taper appears again at the other end.

The DT is simply a mirror image on each end.
If you roll cast past the head, a DT is right for you, the thin running line of the WF can’t transfer the energy efficiently.
It’s in long casts that the WF shines because of the thin running line causing less friction.
For short casts and small stream fishing the DT will be more economical because you can reverse it when the head wears out or gets damaged.

Would like to further point out:

When a  DT line needs to be reversed in a few years,   one will find that the  “new end”  has been coiled rather tightly around  a smaller circle in the reel.            The plastics develop memory due to age,  UV,  heat,  etc.      While I used to be  a fan of  mostly DT lines,  I have scrapped them all.            I always found that reversing a  DT line that was several seasons old usually produced a “slinky”  on the new end that could not be easily straightened, plus, I never got the same mileage out of the now older back end once reversed.

Additional:   With a lot of small stream fishers concerned with having  smaller reels for their light rigs,  remember that using a  DT line with backing always requires  a reel with more capacity =  read:  Larger Reel !      Ex:  one cannot get a  DT-4 line on a  Hardy Flyweight, much less any backing.

And yes,  I believe in backing on all reels, mostly to cut out some of that slinky effect in the shooting line on the back of a WF line.  This means I don’t use  the very smallest  reel  models.

And in this wonderful age of marketing, don’t forget one can look for “standard arbor” reels and make their own large arbors by filling the cotton picking thing with tons of backing.    This is the one downfall of a large arbor. The arbor takes up potential backing space.