For me it's a toss-up between Akroma and Auriok Champion. Ultimately, I gotta go with Auriok Champion.
I feel there are some girls who aren't getting the attention they deserve, though. Here's a few that come to mind:
Savaen Elves, Benalish Hero, Raven Guild Initiate, Vitalizing Cascade, Sorceress Queen.
Please Rate and Comment on my T1.5 Deck - Invulnerability Theory