I'm with Jackster for the reason's he mentioned.
Basically the reason to buy a DT line is for distance and there is very little reason to distance cast a 3 wt line. I went through this exact same discussion two days ago at a Cabela's. His buddies were telling him to buy a WF. We took the WF3F off of the shelf. It had a tip section, a front taper, a belly, and a rear taper before getting to the shooting line.
Streamside Info - Cortland Fly Line Specifications
For a Cortland 444 Classic these add up to about 33 feet. Now add the rod length, say 7.5 ft and a 7 foot leader, and you need to be fishing about 45 to 48 feet from the target before you even get to the running line. Seriously? How often are you going to be fishing over 45 feet away with a 3 wt rod?
The Cortland DT3WT has the identical tip length and 8 ft front taper. Bow the DT and WF will land and fish exactly the same as far as delicacy of delivery is considered. YOU LOSE NOTHING and gain the other end when the first end wears out. You functionally get two fly lines for the price of one.
With a 3 wt rod, you should actually consider a 4 wt line because you may even have enough 3 wt line out of the rod. More common that needing to cast far is needing to cast too short to load the rod with a 3 wt so buying a WF3WT is NOT indicated. You may want to get a DT4WT.
Check the Orvis line specs below and you will notice that model for model, the front taper of a DT vs a WF are identical for the same model line. They will function identically in terms of how they present the fly because the forward tapers are identical.
Fly Line Taper Charts | Reference
The ONLY reason to buy a WF3F is if you need the front taper design that is not available in a DT.
Read what Bruce Richards, the fly line guru of Scientific Anglers says about DT vs WF Floating lines.
Double Taper Versus Weight Forward: Which is Really Better? | Fly Fishing Info Center