Whenever I play WvW I'll usually swap to Staff if we're gonna siege an area, I feel that the benefits (mainly its insane amount of AoE, and the AoE stun you get from air) is too good to pass up. However, if I'm in WvW and I'm roaming (expecting duels or skirmishes with other small parties), I'll stick with D/D as it has much great burst and dps than staff.
However, I've been experimenting with a scepter/focus build and I quite like it. Here's a link to a reddit post about the focus (link). It allows for much better ranged dps than the staff, and complete properly you can get much more burst AoE landed. Seriously: when there's a bunch of eles spamming AirFocus4 it's the most frustrating thing to play against! >_>