I think I would use the sorcerer, with the main gimmick being that each subclass gets a damage type. Every time the sorcerer casts a spell with a damage roll, the sorcerer adds 1 die's roll of damage of the subclass type's damage to the spell's damage. So, if you are a black dragon sorcery sorcerer and you cast fireball, all targets take 1d6 acid damage plus the fire damage. You also get resistance, eventually overcome resistance to the damage type, make it 2 die rolls' worth of damage, and as a capstone, you know one summon spell that you can cast as a 9th-level spell without a spell slot once per long rest (I figure summon spells don't get much use at high levels).
It makes the sorcerer a really good (but simple) blaster, and you can boost non-blasting stuff with the subclasses (plus bonus spells).
Wild magic: pick one of bludgeoning, piercing, or slashing (random objects appear and follow the spell's path); extra good buffing (especially transmutation spells) but the recipient gets a nonmechanical, but weird physical change. Summon Fey as the capstone.
Dragon: Pick one of acid, cold, fire, lightning, or poison. Enhanced spells that change or improve your AC. Summon Dragon as capstone.
Storm: Thunder. Spells that conjure or control water or wind can move things extra far (including the sorcerer moving safely). Summon Elemental as capstone.
Aberrant: Psychic. Enhanced enchantment spells. Summon Aberration or Summon Astral Entity as capstone.
Clockwork: Force. Enhanced spells that affect stuff that people can carry. Summon Construct as capstone.
Shadow: Necrotic. Spells that grant extra or special movement (like teleportation) work even better in the dark. Summon Undead or Summon Fiend as capstone.
Divine (or Spellfire): Radiant. Healing spells work really well. Summon Celestial as capstone.