Jonny Lee Miller for me. I enjoy the portrayal of Holmes as an addict. It pairs his superhuman intellect with human weakness. Benedict Cumberbatch is pretty amazing though.
It's unfortunate that I've never seen the Jonny Miller version but I don't really have any favourite. I mean RDJ'a portrayal is the typical Victorian charm while Cumberbatch adds to Sherlock's sassyness and modernity. I've always stuck to the books more anyway haha