Well, your build is unique. You said you were level 42 right now, right? Your build should be a leveling build then; any one tree works, but trying to take multiple parts of multiple trees does not.
How it breaks down, in the most general sense:
1. Affliction. Runs on dots. Ability to pull large packs and have them all die to dots. Also have some added survivability thanks to siphon life and haunt restoring some extra hp. Downside is that dots take a while to kill, and you'll probably drain-tank enemies, causing higher repair bills. Also not all that useful if you are duoing because things will die quick with two of you.
2. Demonology: Good part is strong pets, and once you get Felguard you have a great all-purpose pet that can tank AND DPS for you. Bad part is lower overall DPS, which isn't a huge concern while leveling but is in raids.
3. Destro: You're a mage without the slows. High mana use, high burst. Might work out very well with two of you, because any target will drop dead before reaching you.
Again, that's generalizing. At max level the game will change, but right now affliction is the best DPS spec (although it suffers from a few bugs, making more than a single affliction 'lock in a raid a slight nerf).
Solo, I leveled my warlock to 46 drain-tanking as an affliction build. I liked it. I think, if I still played him, I would go Demonology once I could take Felguard. Destro simply never appealed to me.
What posts are you looking at? Elitist Jerks has some very good ones, if you're looking for raiding. For leveling, any advice is good because all of it is anecdotal; people like to level different ways and no single way is necessarily "better" than another.