D/D or staff?
I usually alternate weapons depending on what I need to do.
Overall best damage is the staff. However, it is hard to use, and requires a lot of experience/proper positioning, and luck as highly mobile enemies will run right out of your range and you may end up charging yourself right into a damage patch. Vault’s ability to dodge is extremely valuable, though.
The low maintenance option is D/X. The dagger auto was buffed recently, so in an auto attack war it beats out staff. I haven’t used the dagger in awhile, but I believe the rotation is still CnD → Backstab → two auto chains. The damage buff from revealed is good, as well as the aggro dropping, and heartseeker spam in a smoke field is excellent finishing damage. But, if you want more group support, off-hand pistol is good for blinding mobs and breaking bars.
Sword is the most “supporty” weapon of the bunch. The biggest advantage is the spammable condi cure, so sword/x is good in places with high condition damage. Pistol whip is also good for self preservation, and in those rare cases where you need boons gone but nobody can remove them for some reason, Sword/Dagger still has use. Most likely this will be the least used set, but don’t forget that it is there.