Best SPEC for PVE and best SPEC for PVP for pure dps or utility in raids

Title says it all.
Affliction vs Demo vs Destro For PVP (mostly Arenas or World PVP)
Affliction vs Demo vs Destro For PVE

The reasons why warlocks are wanted in raids:
1. SS (Summoning Stone)
2. Spell power buff
3. SS (Soul Stone)
PvE wise Demo > Affly > Perhaps another class > Destro.

For dps Affliction, for versatility / buffs demo.

PvE:
If you have end-game gear and want to do good DPS and lose some hair in the process go Affliction.
If you want to buff the raid in your medium / endgame gear go Demo.
If you have **** gear and you can't really buff anyone because your SP is low but somehow your cousin invited you to raids. go Destro do perform terrible DPS but less terrible them Demo/Affli would do in this kind of gear.

PvP:
I'm going to discuss Destro vs Affli first.
I can't really say that one is better then another, it all depends on situation.
I've played both of them so long and so much and I still can't say I prefer one over the other.
For WPvP and BG's it all comes to personal preference.
If you like burst and big numbers and that explosive play-stile while listening music from 2009 WoW PvP videos go Destro, you will love it.
If you like smart game-play that can put big pressure to multiple people and keep you alive for long time then go Affli.
If you are really new to Warlock in general I would suggest going Destro first because Affli in general in kinda hard to play, especially in PvE but in PvP as well.
For arena not much to say. Your spec depends on comp you are playing. I would suggest having both specs if you are focusing on arena so you can swap them depending on what situation you are in.

Now to Demo PvP. There is a reason you don't see many of these.
People say that this spec is not viable for PvP but they forget that this spec belongs to a Warlock, and if we managed to tank ****ing Anub'Arak ( https://www.youtube.com/watch?v=RS-mk2WMq8I ) then we can manage to make this work, and we did.
I myself do not have a huge experience with the spec in PvP, but I do have it nonetheless.
PvP wise, your biggest advantage is element of surprise.
Everyone expects a chaos bolt and haunt guy but barely anyone expects a demon charging in their face.
The other day I queued arena with my low geared friend to help him a bit and this happened to me.
Needless to say, I was shocked.
I've seen it performing very well with a hunter. Not sure about other comps, If anyone would suggest some that would be great.
In WPvP / BG is can be awesome and you can kill people so fast sometimes but they can also kill you as well. I would suggest bringing a pocket healer in this case.

Hope this wall of text helped you at least a bit.

Cheers.

And if uwanna some less common opinion: demo pretty close to affli in terms of dps, i mean overall icc damage , not just few bosses (u have more aoe burst for trash, oportunities to roll execute on mobs, and u are not forced to ignore tactic to "not loose dps on dbs adds etc") U can check it yourself.
If not rollef corruptin with tot from rogue.
destro/hybrid are just boring.
And affli is not so hard as ppl are saying, if u know dots mechanics and roll it ( this spec has a lot of gaps to moove between insta casts, compare to other specs). Demo in comparisonhave less amount of theese gaps, but ezier rotation.