I would have to choose a combined army of Slivers, from Magic: The Gathering, and the Borg, from Star Trek.
The Slivers come in myriad types, each with its own special ability, such as multiple heads, spell immunity, stronger muscles, heightened reflexes, flight, regeneration after death, and even the ability to feed me mana instead of attacking.
They are birthed by the Sliver Queen, who can hatch a new, combat-ready sliver for a mere two colorless mana, and they are led by the Sliver Overlord, who can assume control of any Slivers who happen to be separate from the Hive. The Amoeboid Changelings assist the Sliver Overlord by transforming any other creature into a Sliver, allowing the Hive to assimilate new creatures.
Best of all, however, are the Slivers' unique trait of sharing their abilities. Every Sliver shares its special ability with every other nearby Sliver ~ if you have a spell-immune Sliver and you summon a two-headed Sliver, you now have two spell-immune, two-headed Slivers.
The Borg Collective is made up of drones assimilated from almost every known species in the galaxy. They are equipped with advanced technology, ranging from strength-enhanced prosthetic limbs to ocular implants that greatly improve a drone's visual acuity, even allowing image processing effects like night vision, thermal vision, and magnification. Their best piece of tech, however, is the Borg Adaptive Shielding. After taking damage, these shields adapt to the type of damage taken, granting complete immunity to that type of damage. Each drone also possesses assimilation tubes, extendable syringe hoses that inject Borg nanites into any living creature, replacing its biological systems with technology and taking control of its brain, turning it into a new drone.
They are led by the Borg Queen. She was the first Borg, and the cortical implants in her brain store the collective knowledge and technology of every species the Borg have ever assimilated. She is an expert tactician, even possessing Captain Picard's tactical skills.
Each half of my army will have assimilated the other half, granting the Slivers superior technology and near-invincible Borg adaptive shielding, and granting the Borg access to all of the abilities and powers of nearby Slivers.
I suppose I would be the Borg Queen, leading my army of Borg Slivers to assimilate everything that ever existed.
WE ARE SLIVER OF BORG. RESISTANCE IS FUTILE. YOU WILL BE ASSIMILATED.