These four are what I believe to be the best choices for a deck portraying one of the greatest protagonists of our generation.

I will grade them based on the same factors from gilgamesh options with flavor and usability.

Due to the significant connection Sephiroth has with those of Angelic references, such as angels and seraphim(specifically safer sephiroth), I focused my selection to those with a Angelic connection.

I will start with the best option in the colors you selected. You gave a suggested color combination of W/B.

The only Angelic in nature individual that was represented by those two colors alone is Selena. She is an interesting card, but lacks raw power that obviously sephiroth embodies. She does represent the idea of him well as she is currently the only legendary Angel that carries this enemy pair of colors. Sadly I didn't search hard, but I am not aware of the history or story relating to her. Although I haven't quite given this particular color combo a lot of thought I feel that the white would be excessively white with only a smaller portion being black cards. Flavor=4 usability=3

Up next are the two three colored generals.

First is Kaalia. Kaalia is unique in a number of ways. First she is not an actual angel in creature typing. Secondly she incorporates the colors I feel would optimally fit sephiroth. I would go into another color pie rant, but simple break down is W=Law/order R=emotion B=self-interest. Thirdly Kaalia is unique as she can summon another Angel, demon, or dragon when attacking. Although this can be interesting and really powerful, as in oppressive, it also doesn't fit the theme well. Two of the three types are flavorfully as Dragon's often surrounded Sephiroth and his lairs and angels for his own embodiment. The demons kinda have a place, but due to what I have seen these decks do, the moment you play kaalia it's either win or get every following creature destroyed. I had a friend build a deck around her that once she hit tue table it was target her until she was too expensive to play anymore. Flavor =5 usability=7

Second to last is Tariel, Reckoner of souls. She gets a better score from me than Kaalia. She embodies the major pieces of the color pie I feel sephiroth falls into. Artistically she looks closers visually to the one winged Angel. She bears an oversized weapon with black wings. She bears a good stat set but lacks in the power department. Sadly all three of the above creature do not share a major part in magic story with Kaalia and Tariel being released as stand alone products. Even with Tariel`s good looks, the ability she has is not really flavorful. Although sephiroth has remnants that he can use, he doesn't really have the power to bring back the dead. Flavor =6 usability =4.

Last, but certainly not least is Avacyn. Avacyn is the creation of Sorin, designed to protect the people of the plane innistrad. She bears great power and responsibility. In the time after her release from the vault she has a decent into madness. This is due to the infection of her mind by Emrakul. Emrakul is a great eldrazi and is rather alien to all planes she transverse. Emrakul much like Jenova came from another world and infected, albeit much much later than sephiroth. Avacyn is also predominantly left handed like myself and sephiroth. In multiple cards portraying Avacyn she can be seen holding her spear with her left hand, although in some she can be seen holding the Spear with two hands. Luckily Avacyn`s weapon is similar in nature to the masamune. It is a long weapon and gracefully has a card of its own. The major draw to this Avacyn is the duel nature of the card. The white side shows off the "warrior" the hero of war that I know Sephiroth was in the events prior to the FF7. The red side shows the side of sephiroth we all know after his decent into the madness brought on by Jenova. I feel she was the perfect fit because of the duality in the card and the other major connections I was able to find. The abilities even work well with the deck. Flavor =9 usability =7