I chose
Sorin, Lord of Innistrad. Without planeswalker removal, he can be a beast. By generating 1/1 lifelinkers he does a very good job protecting himself (and in W/B, you should have plenty of cards to help with that,) and giving all your guys +1/+0 every third
turn can generate massive amounts inevitability. And he's reasonably costed at 4 mana.
I also love Elspeth, but more for her art, lore and ultimate than her real world usability.
Don't underestimate the card advantage machine that's
Jace Beleren either. I think he's undervalued and at $8, a real steal.
And since I apparently love Planeswalkers soooooo much, I can't stop!
Liliana of the Veil is an immense powerhouse in any tight format, (such as Modern.) When you're running in a format like that where every land drop, creature and response matters so much, repeatable saccing and discard is often just too much to handle. I have more of a hate than a love relationship with her (mostly since I don't have her, so I'm always on the receiving end of that
bargain.)