A High elf character, at that?

I'm thinking Lord Stone with extra defenses, but I'm not sure. Atronach gives you 5 levels worth of magicka, but regen is compromised.

Thoughts on the best Standing stone for a mage?

(I'm not interested in leveling my magic skills faster, either)

I just always do the Lord no matter what character I'm using. It requires no special considerations, no one-a-day-powers you might end up forgetting about, and it's not one of the "Make the game 20% faster ones." Bonus armor on an armorless class, and being able to approach the Spell Resistance cap without being a Breton are always plusses when you spend most of your time fighting other mages to prove you're better.

Although for the sake of "theme", Atronach is at least interesting, and The Ritual could add another layer if you're playing someone who isn't shying away from Necromancer.

Atronach. The extra 50 magicka is nice, the 50% spell absorption is amazing. With the atronach perk you can get 80% absorption... and with a necromage you can even hit 100% spell absorption(people say they capped it at 80%, but I've tested it with my necromage and he is completely immune to magic).

Regen isn't really important. Your regen drops to nothing in combat, so more magic > higher regen. And even with 50% regen there is normally enough time between battles that it still refills to 100% without having to wait around.

My favorite... 50 more magicka means 5 levels that would have went to magic can go to health instead, so your character has 50 more health which can be life saving for a mage. My mages with atronach stone always put the first 10 levels into health for a good early game boost, and rarely do I have any magicka problems.

Atronach is ridiculously powerful. The regen isn't that big of a deal when enemy magic is recharging your magic bar.

But there is one problem...if you use conjuration, having the atronach sign(or any magicka absorption effect) can cause you to absorb your own summon spells.

And does the ritual power dismiss your other summons when you cast it?

Aetherium crown+atronach stone+the apprentice stone=one happy mage.

Do you have "boxes full of pepe?"