1H warlock is good. Definitely farm 1H. If not dont choose warlock at all.
Question here : 2H,DA... which one is better to compliment 1H warlock?
Well, I would choose (upps, choosed already

) DA over 2H.
Why?
PvP: Because, you are already good at PvP, not really need 2H or DA here.
PvE: 2H kills any single target faster than DA. But, DA kills any multiple targets faster than 2H. DA has skills that hits multiple targets, with no KD,KB, it really kills faster. (Try 2H and DA at ongs, you will understand what I mean).
If you choose 2H, you can use it even against party mobs easily. On the other hand, with DA, you mostly hide behind 1H\s, and wish for a cleric support. But you are still good with 1H, so not a big problem.
Final words:
1H\2H warlock will be good against any single target. You will have to deal with multiple targets one by one.
1H\DA warlock will be good against both single and multiple targets.