As you might imagine, the guests at InStyle's annual Summer soiree were a pretty well-dressed crowd. The who's who of Young Hollywood offered up the trendiest kind of cocktail ware on last night's red carpet — now, we're taking a closer look at who wore what.Christa B. Allen arrived in a sleek, black strapless dress with a split neckline, graphic-print clutch, and metallic cap-toe pumps. The newly engaged Ashley Tisdale opted for a bold printed minidress and jeweled drop earrings, which she finished with a pair of peachy, classic pumps. Analeigh Tipton's minimalist cream-white jumpsuit offered a totally different take on partywear, and Julianne Hough may have just been the dressiest of the evening in her fishtail, full-length Halston Heritage skirt and white Bec & Bridge top. Speaking of superlatives, does Katie Cassidy get your vote for sexiest of the night? We think so — with that slashed cutout and tough nail hardware (and studded heels!), Katie's LBD is one part tough girl, one part vixen. Playing opposites, Isabel Lucas's lace top and floaty maxi skirt spoke to a softer side, albeit with nods to the '90s, thanks to her black beanie cap. And Ashley Madekwe glowed in her own '70s-inspired yellow jumpsuit from Diane von Furstenberg's Spring '13 collection, while Brittany Snow was sweet in a Lela Rose dress and coordinating nude platforms. Now that you have all the information, it's time to make an informed decision: which of InStyle's party guests was most, well, stylish?