If you have Aerie and your PC Mage/Sorcerer...

knight1337

Who should get the Robe of Vecna?

Hard choice, Aerie is awesove with the robe but your main char too..

That's why I always play with 1 mage only, and usually no Aerie in the party

SionIV

I would always give it to your main char if he is an arcane caster. With the exception of Edwin your main character will always be stronger than an NPC's.

elminster

I'd give it to Aerie until we hit 3 million xp. At which point I'd switch it over to me (by that point Aerie has a number of triggers she can instantly cast).

Corvino

Your main is going to have access to Improved Alacrity first, which is where the robe really begins to shine. I'd use it on the PC in this case.

booinyoureyes

I feel like some nice cleric spells take forever to cast, so earlier on I'd give it to Aerie (I'm planning on doing this in my current run, actually). For example, Prayer gives some decent buffs, but has a casting time that is simply not worth the benefits when cast in battle. The Robe changes things completely. Also insta-healing is kinda fun.

Yet as soon as you get Time Stop plus Improved Alacrity (or even just Improved Alacrity) then you become a Machine Gun of Doom when you have the Robe of Vecna on your wizard/sorcerer

jacobtan

I'd go with PC if he's a pure mage/sorcerer. Clerical buffs can be cast as preparation before a fight but in the heat of battle, a pure mage/sorcerer with Robe of Vecna would be better positioned to deal damage or debuff, compared to Aerie.

vish

I put it on whoever my main spellcaster is. Aerie is very good with it since she has access to Cleric spells, but overall she doesn't get "great" use out of it. The best things she can do with it are healing spells. I honestly hate Aerie with a passion.

Blackraven

I'd always keep it on Aerie, for the reason @booinyoureyes mentioned. In general, arcane spells have much shorter casting times than divine spells.
Some people suggest switching the robe from Aerie to charname in the late-game, once the HLAs become available. But a mage with Time Stops and Improved Alacrity doesn't need the Robe of Vecna to be unstoppable.

IMO the Robe of Vecna is made for cleric/mages.

Corvino

Reduced casting times help you make the most of the more-than-one-spell-per-round opportunity that Improved alacrity offers, as you can fit more spells into the duration. A Mage with Timestop/AI will kill stuff without it, but is an ungodly creature of destruction with it.