I'm starting my first character, a high elf pure mage.I'm thinking to focus on conjuration and destruction - is there a clear winner at high levels between fire, lightning & cold?

I'm thinking that the obvious thing to do is to summon a atronach matching the type of destruction magic preferred, in doing so does it make it pointless to have followers? I.e. if your specializing in destruction magic do AOE spells make it hard to avoid killing your followers?

Storm Atronachs are the strongest elemental atronachs, I think.
Shock spells have a perk that can disintegrate an enemy when their healths reaches ~10%

Followers wearing armor will move plenty slower than a mage in robes so they may not be able to properly tank, and really dont choose one that has some skill with a bow, as they may shift to their basic bow and attack at range, even if they have an ebony sword and shield. Man, Lydia and be so dumb at times...I mean most of the time.