For WvW solo or small group roaming, D/P or S/P is generally the way to go in my opinion. D/P has the better dueling potential, while S/P is significantly better at soloing supply camps. The cleave on S/P coupled with the defense of Black Powder (and the evades on Pistol Whip) make it one of the easier specs to solo a camp with, across all classes, in my experience. Daggerstorm is nice for soloing camps as well, but can obviously be run with any set of weapons.
Ultimately though, play both builds (or try some others if you wish) and decide what you like to play. S/P is better at capping camps, but I personally don’t like the playstyle as much, and thus don’t play it often. A friend of mine who I roam with frequently (though not always on my thief) really enjoys D/D, and he still captures camps.
Another thing to consider is that capturing camps is, in my opinion, far less important than performance during an actual fight. I’d rather have a build that’s terrible at capturing camps but awesome against other players than the a build where the opposite is true.
