Our PicksFrom Kate Middleton to Rihanna, The Best and Worst Dressed of the Week (PHOTOS)Isabel Wilkinson03.29.13Our PicksFrom Kate Middleton to Rihanna, The Best and Worst Dressed of the Week (PHOTOS)Kate Middleton experiments with hats, Allison Williams looked prim in Oscar de la Renta, and Rihanna goes sheer. See the fashion highs and lows of the week.Isabel Wilkinson03.29.13 7:00 AM ETImeh Akpanudosen/GettyBest Dressed, She Who Can Do No Wrong: Kerry Washington Kerry Washington perpetually tops our weekly list – and this week was no exception. She looked prim in a black Jason Wu bustier dress at the Human Rights Campaign Gala in LA on Saturday night. Larry Busacca/GettyBest Dressed, Prim and Proper: Allison WilliamsMarnie, for the win: Williams looked pretty in an Oscar de la Renta dress, Roger Vivier shoes, and Colette earrings at the premiere of HBO’s Phil Spector in New York on Wednesday night. Andy Stenning/AFP/GettyBest Dressed, Like We’ve Never Seen Her Before: Kate MiddletonIt’s not that this outfit is stylish as much as it is adventurous from the typically by-the-book Duchess. During a snowy sausage-cooking sessions with boy scouts in Cumbria, Middleton wore jeans and rain boots–and a newsboy cap. Rabbani and Solimene Photography/GettyBest Dressed, Hint of Skin: Zoe KravitzAt the Swarovski Crystallized Launch at the Gramercy Park Hotel last week, Kravitz looked spot-on in an all black Alexander Wang dress and shoes from his spring collection. Richard Drew/APBest Dressed, What A Dream: Tilda SwintonSleep no more: Swinton could have been wearing anything as she slept during her spontaneous, one-person performance art piece at MoMA this week –but, just by being Tilda Swinton, she looked downright cool. Pascal Le Segretain/GettyBest Dressed, Full Bloom: Natalia VodianovaThe model channeled spring with a floral Dior dress at the Bal De la Rose Du Rocher in Monte Carlo last week. Stephen Lovekin/Getty Best Dressed, Blue Mood: Saoirse RonanRonan looked radiant in a blue Proenza Schouler dress at the Cinema Society screening of The Host in New York on Wednesday night. Felipe Ramales/PacificCoastNewsBest Dressed, Peplum Rally: Karolina KurkovaThe model strutted out of NBC (where she was promoting her show, The Face) on Tuesday in a marigold dress by Polish designer Karolina Zmarlak, which she accented with a nude belt. John Stillwell/AFP/GettyBest Dressed Couple, Unsurprisingly: Stella McCartney and Alasdhair WillisWell this one is a no-brainer: Stella McCartney and her husband Alasdhair Willis showed up at a ceremony (where she was given an Order of the British Empire) at Buckingham Palace looking pretty spiffy. Jon Kopaloff/FilmMagicWorst Dressed, What in the World!: Ke$ha Ke$ha looked like Flava-flav at Nickelodeon’s 26th Annual Kids’ Choice Awards in LA in a light blue tuxedo and a cane. George Pimentel/WireImageWorst Dressed, See Thru Shorts: RihannaIt may be Givenchy, but Rihanna’s concert outfit in Toronto last week was pretty wacky too. Frazer Harrison/GettyWorst Dressed, Shield Your Eyes: Ryan NewmanThis sour cupcake showed up at the Kids’ Choice Awards, where she perfectly matched the color scheme on the purple carpet.