The biggest deck I would be worried about when registering U/W Spirits is Mardu Pyromancer, due to the combination of removal spells and Lingering Souls
With Walking Ballista already a primary inclusion, adding Aerith isnt too far-fetched
He can be Shifted for a reduced Ink cost of three, and he has abilities that make him well worth getting in play
In fact, I know you can, because the other commander for the Tyranids is already much higher on this list
Thorna and Twigtooth is an aggressively costed Arena-only commander, sadly you won't remove many stun counters with its attack trigger, but otherwise, any cool drawback counters you want to get rid of become a huge advantage for you
Sauron, the Dark Lord Sauron, the Dark Lord is a very strong threat on its own