Vivian is the best cleave option available. Her S3 provides a self Greater Attack Buff, Immunity, and a team-wide attack buff, fulfilling a large number of requirements. In addition, her S2 is a strong cleave that clears both the 1st wave and the eggs reliably.
There are two different builds available for Vivian, either a 180 Speed or a fast 228 Speed build.
180 Speed:
By using her EE to gain 50% CR after she casts her S3, Vivian can reliably cut the slow nukers and S3 -> S2 on the first wave. With this build, 180 speed is a minimum and should be adjusted to be 155% faster than your nukers. This build should be ran either with another Hero at 228+ speed with Immunity or Stun, or with your entire team on Immunity set.
228 Speed:
Adding additional speed allows Vivian to go before the 1st wave, setting up her Immunity buff before the Striker Warlords attack. However, this comes at the cost of some damage. This build should be ran in setups where you do not have another Hero that can Stun or provide Immunity.
Gear Requirements:
Vivian’s S2 is a decent AoE, but cannot cleave the 1st wave reliably, As such she should be paired with another cleaver or Defense Break.
Decent benchmarks are 3500 Attack, 280% Critical Damage, and 180/228 Speed. This provides enough damage to fully cleave with Defense Break, and always one-shots the eggs. When paired with a second cleaver, this is enough damage to clean up the wave and proc Time Matter for the Azimanak fight. Note that with these stats, she may not be able to do enough damage to the Karax Charger unless Striker Warlords are left alive for her 2nd wave to proc.