I think there is probably still a good article in the archives here by Leon Chandler, who was Cortland's ambassador to the fly fishing world. See if you can find it.

The gist of it, as I recall, was that you will normally have no difference in your casts until you get to a distance where the weight forward's running line (the thin part) comes into play. I fish streams, so runnig line never comes into play for me. If I tried to fish at a distance where I was into my running line, I would not be able to get a good drift. So I buy DTs as they have the advantage of being able to be turned around on my reel when the first end gets worn out, thus doubling the effective life of my fly line.

Many catalogs will show you the profile of the lines they offer. If the line profile looks about the same for WF and DT at the distances you cast, I think DT is your best bet.