Invoker and Aghanim?

I personally don't buy it and prefer going for "INT carry"

Absolutely core if not going for quas wex, I mean in a general fights i end up using around 6-7 spells easily.
I prefer the forge spirits build so really get aghs rights after I hit round level 12-13 by that time I have a necro 3 , boots and drums and wand.
Sometimes I go the max exort build depending on the situation and get a bkb way earlier, then i proceed towards aghs.

Some might say the 2 sec cd is not that great a buff but it really adds up in big fights.

I used to get Agh's on Invoker, but I realized the biggest problem I have when playing him is not invoking spells, but finding one off cooldown in the middle of a fight: most of the time I can land my Tornado- EMP/ Chaos Meteor- Deafening Blast combo, after which I can only use Cold Snap, Ice Wall, Sun Strike and maybe Alacrity ( Ghost Walk too if I have to run away), most of which need a good opportunity to be used well. Plus, Forge Spirit should be activated before fighting, so you don't need to Invoke it a second time.

I prefer going QW though, being able to gank past level 6-7 is really strong in pubs. And I sometimes use it in team matches, too: EMP mana drain is still strong in my opinion.

My general combo goes like this(not counting spirits, they are pre-summoned) , Tornado, Meteor, Dblast, EMP (then refresher if i have ,another def emp ) After this coldsnap, alacrity and SS are usefull for finishing off people, but mostly none live after this except 1 or 2 guys. I really like having the aghs for this combo as it lets me get off that emp fast enough ( As for why I emp fourth is to regain mana and not so much for damage)

As for preference, dont consider this rude but I dont really find QW at all a challenging build, its way too easy and the skill ceiling for that is pretty low, though you can do monstrous things with a right tornado, I once cancelled 2 ulties with it, real fun.

My preference is always with exort builds as they let you use other spells, while exort spells tend to rely SOLELY on exort for damage and I use the others for the debuffs. Mostly as soon as level 11 i have 10 spells to use which is much more as compared to QW( no 1 will use exort lvl 1 meteor now will they? maybe to scare someone, but only against inexperienced guys).

Though I play what fits the game, If i have a lycan or NP on my side, I go QE ; If the enemy has mana dependent heroes I do go QW, and if the enemy is all squishy and i'm feeling particularly baller I go for EW which is a high risk high reward build.