Enver Gjokaj was, by far, the most impressive actor on Dollhouse. All of his imprints had very distinct touches, and his skill with accents is uncanny. But as Chainsaw and 005 said, he didn't so much impersonate Fran Kranz as channel the guy. Every mannerism and vocal inflection was dead on. Seriously loved it. I wasn't generally wowed by Eliza Dushku. She's hot and everything, and kicks ass, but I think Dollhouse revealed a lack of range in her that I was disappointed by. It didn't help playing against Enver the Versatile.