To be brief, I'd like to see you rework #3 to fit some other elements from the first two (and to clarify the setting), while avoiding confusion. My suggestion would be something like this:

Conned into destroying the last city of a futuristic Earth, clairvoyant Aviva has left broken hearts, a war, & a deadly pandemic in her wake. To save what’s left of humanity, she must defeat the synthetic god who tricked her to begin with.

If you have space to better explain "Synthetic god" (android? AI?) in a single word or two, that might be nice as well.

Individual notes on the pitches:

#1 Leaves me too confused:

The last city burns, Aviva its torch. Asking too many questions here. Last city where, and how is she a torch? She thought her clairvoyance would be their whose? salvation but was blind to the synthetic deity ??? manipulating her. To save whats left of a crumbling world she’ll steal God’s throne ??? for herself. #2 Still confusing, but first line was good.

Conned into becoming an avatar of destruction Aviva ends the Last City last of what? beneath the heels of an android revolution. But war has no winners. What is this phrase doing here? A virus is her death knell how so? unless she slays the synthetic God who used her from the start.

#3 Generally cleaner/less confusing.

Clairvoyance hasn't helped Aviva escape disaster. She's left broken hearts, a war, & a virus that's eliminating the last of humanity in her wake. But she might save what’s left of it by taking God’s throne for herself. Not sure what you mean by "God" here.