DS or Wells?
You can combine both in a 0/20/0/20/30 build for example and that’s very effective in zerg WvW play. If dungeons are your top priority, you should roll one of the classes more useful in that kind of content though to be honest.
As said above, you can have both and still be very effective. Here is the build I currently run for large group WvW:
The #7 Utility is kind of a floater depending on the situation, and I sometimes have Chilling Darkness traited instead of Banshee’s Wail. I also sometimes change some traits for LB focus build when fighting unorganized or non-guild forces.
Zend(ario/imas/iana/ango) – Engi/Ele/Necro/Guardian
[KnT] – Blackgate
[KnT] – Blackgate