For what it's worth (not much), Huffington Post has a poll where you can vote on which film actors and actresses pass best playing the opposite sex. You can pick the top five from 24 nominees and currently, Cillian Murphy in Breakfast on Pluto is in the lead.
It is not a very good poll. Some of the nominees are there because of their notoriety and not their femulating skills. As a result, there are some major omissions, for example, Wesley Snipes and Patrick Swayze from To Wong Foo Thanks for Everything, Julie Newmar are among the nominees, but their fellow drag queen, John Leguizamo (photo above right), is not among the 24, and in my humble opinion, he passed the best of the three.
Also missing are Steven Mackintosh from Different For Girls, Robinson Stévenin from Transfixed, Michael Cavadias from Wonder Boys, Adrian Pasdar from Just Like a Woman, Helmut Berger from The Damned, etc., etc. etc.
I can come up with many more who are more deserving and I am sure you can, too.