I feel like this is a very straightforward answer.
I want to run down some stuff in my mind.
Alexander doesn't have anything too surprising, most of his stuff is very straightforward, nothing very surprising. S-2 on the other hand is a different story. She has the ability to manipulate her swords at will and has telekinesis.
In my mind the two of them would lock weapons, Alexander clearly has the advantage in terms of weapon match up, a katana vs sword & board is very much in his favor, but I can see her lock her blade with his. In this instance, she could telekinetically push his shield slightly to the side and increase the length of her blade, and stabbing Alex in a vital area.
Even if this scenario doesn't play out, she has force-fields which Alex would have to try and buff himself to try and get past while she can set up a telekinetic riposte with her katana as he tries to push his offensive. His energy projectiles would normally be an issue and force her to focus on dodging rather than attacking, but force-field with telekinetic sneak attack with a surprising extending reach... yeah I just think she has ways to catch Alex off guard while Alex doesn't have the same.
My vote goes for S-2.