Lightning Hammer Weapons: S/F, S/D or D/D?
Focus provides the same number of blasts as offhand dagger, they’re just spread out over more attunements. Offhand dagger can provide an easier to use fire field for someone just learning to blast might with scepter. However offhand dagger does not have the defensive utility that focus has (but dagger does have a good amount of mobility). Focus can provide a wide area projectile block, as well as a personal reflect and invulnerability. Mobility is usually not widely needed in dungeons, so offhand dagger is not an optimal choice.
Scepter vs main hand dagger:
Scepter is a highly single target weapon, but it has an extra blast and some utility in the form of self condition removal that comes with vigor, and a buff to toughness that can be kept up permanently.
Main hand Dagger is an excellent weapon for cleaving (lightning whip) and does not rely on lightning hammer for its damage. It is a more optimal choice for extended fights when you cannot rely on the second lightning hammer to be left untouched.
If you really want to squeeze all the might you can out of your prestack, swap out Focus/Off Hand dagger for the other one before a fight to get 1-2 extra blasts in earth, then quickly swap back before engaging.
I personally enjoy Dagger/Focus for pug runs, since I don’t want to rely on a Lightning Hammer that may or may not be there when I need it.
Thanks a lot for the response! That was all the information I needed and then some I might try out D/F then and see how it goes.