Re: DT fly line.
You will no doubt get lots of response to this question. In short the DT line has a heavy belly and a taper on both ends. They cast well and mend / roll cast very well due to the weight in the belly of the line. WF's have a taper followed by a short belly then the rest is essentially running line.
It is really a matter of choice for you based on experience with the various lines. We can spend time splitting hairs and discussing what lines are used in casting tournaments or use what ever feels good to us. I use DT's on almost all my rigs and don't seem to experience any of the problems that people describe having with them. Yes I sometimes cast long too. When I first started buying quality lines they were almost all DT and you had to search for a 'Rocket Taper' then the market decided that weight forward should be the line of choice and DT lines became scarce. The same thing happened with down locking reel seats. Almost all the rods I bought pre 1985 were down locker's then suddenly they were all up locking seats. Being a sort of eccentric I have changed some of my seats on favorite rods to down lockers and bought enough DT lines to last me through the next swing in the market.
Others will disagree with my assessment on lines but then I'm just some guy who fishes and writes his biased opinions on a fly fishing forum, I am not certified by anyone or any organizations as an authority on lines or rods.
My advise, try one.