Each warlock tree has their own strong points, so there's no such thing as a single best build. However, it looks like the next patch is going to make Demonology even more powerful for PvP, and Soul Link is just insanely powerful in its current form. A 31 Demonology, 20 Affliction like the one below is probably one of the more reasonable ones for surviving and farming CP at a reasonable rate.
Affliction Mastery
Suppression Rank 5
Improved Corruption Rank 5
Improved Drain Soul Rank 2
Improved Curse of Agony Rank 3
Amplify Curse Rank 1
Grim Reach Rank 2
Nightfall Rank 2
Affliction Total: 20
Demonology Mastery
Improved Healthstone Rank 2
Demonic Embrace Rank 5
Improved Voidwalker Rank 1
Fel Intellect Rank 5
Improved Succubus Rank 3
Fel Domination Rank 1
Fel Stamina Rank 5
Master Summoner Rank 2
Demonic Sacrifice Rank 1
Unholy Power Rank 5
Soul Link Rank 1
Demonology Total: 31
It's not a perfect build - you'll need a bunch of +shadow damage and +stamina gear for it to be reasonable, and more points in the new version of Imp. Voidwalker would probably help for bandaging between voidwalkers when soul linking - but you can do reasonable damage and come out of it alive.
Affliction Mastery
Suppression Rank 5
Improved Corruption Rank 5
Improved Drain Soul Rank 2
Improved Curse of Agony Rank 3
Amplify Curse Rank 1
Grim Reach Rank 2
Nightfall Rank 2
Affliction Total: 20
Demonology Mastery
Improved Healthstone Rank 2
Demonic Embrace Rank 5
Improved Voidwalker Rank 1
Fel Intellect Rank 5
Improved Succubus Rank 3
Fel Domination Rank 1
Fel Stamina Rank 5
Master Summoner Rank 2
Demonic Sacrifice Rank 1
Unholy Power Rank 5
Soul Link Rank 1
Demonology Total: 31
It's not a perfect build - you'll need a bunch of +shadow damage and +stamina gear for it to be reasonable, and more points in the new version of Imp. Voidwalker would probably help for bandaging between voidwalkers when soul linking - but you can do reasonable damage and come out of it alive.