The voidwalker is kinda weak, one crit will change the agrro to you. The only reason to use the pet is to sacrifice it, but thats my view on it. At lv 50 you can get a quest which will get you a trinket that lets you summon a voidwalker without using mana + shard. I think they did it because the pet sucks :P
Demonology kinda means that you have to depend on your pet + it eats shards away like crazy. I went for the mage build, Affliction > Nightfall and almost full destruction (I do have conflagrate). And I must say that I like it, but the chance of surviving with demonology is greater I think.
But like I said My warlock is messed up, it does loads of damage, almost the same as a mage (not counting the DoTs) and my health is 4900 and my mana is 4400. But health = mana (just takes some time to convert). I guess demonology is more fun to play with but in mass pvp you will be owned like hell.
And putting points in Improved voidwalker is eh.. crap
but this all is my view on it so pleae prove me wrong and discuss
