Just the night before, Rooney Mara joined sister Kate on the red carpet for the premiere of her new show. Now Kate is returning the favor. The actress stepped out for the NYC premiere of Rooney's new film, Side Effects, and even followed up with a sweet tweet about her sister's performance. Aside from the family bonding, the sisters' arrivals again gave us a side-by-side comparison of their personal styles. They set the stage for a style battle with obvious contrasts. Rooney opted for a creamy white Alexander McQueen confection and Kate stepped out in a flirty LBD. But color palettes aside, there are a few common denominators. Each dress boasts a feminine fit-and-flare shape and a more fashion-forward cut. Kate's is certainly a more understated look, and the true beauty of Rooney's dress is in the gorgeous floral appliqués and embellishments. Rooney is also the first to bring McQueen's Pre-Fall '13 collection to the red carpet. As for the finishing touches, Kate looked to a sleek metallic clutch and Nicholas Kirkwood platform pumps with a little more personality, while Rooney let the gorgeous dress take the focus, also choosing Kirkwood heels, but more pared-down, nude peep-toes. That's the fashion breakdown. Now, study up and cast your vote for the sister who stole the spotlight on last night's red carpet.