I'm using an Archon build at the moment. Due to a set bonus I have, every time I deal damage outside of Archon form, I gain a stack. I can gain up to 20 and once I enter Archon, I consume all stacks and radiate enormous amounts of damage scaled to however many stacks I had upon activation. Which spell or spell/rune combo will get me to max stacks the fastest?
Arcane Torrent with Static Discharge rune is what I see most often.
Static Discharge makes Arcane Torrent split so you have more projectiles that hit enemies with each basic attack while outside of Archon form. This is the best way to stack charges that I've played with. This is also a fast casting spell so there is no need to 'charge' other Wizard abilities.
IIRC I was using a similar build to this and what I did that seemed to work fairly well was using Disintegrate with attack speed bonuses on my gear. Since Disintegrate goes through multiple enemies, you get a tick for each enemy hit, and the higher your attack speed, the faster it ticks. The only issue with this method is maintaining enough arcane power, but there's ways to mitigate this as well e.g. arcane power on crit, bigger arcane power pool, etc.