Benedict Cumberbatch. His character, primarily due to the writing, I feel fits with the original character. As well he exhibits that arrogance you expect of the character with the same fallibility when he might fail.
Downey's character was ruined for me with his detailed deconstruction of a fight and the physicality of the character which I understand many others find fascinating. Plus it fits with Guy Ritchie's direction. I enjoyed his character.
I admit I have yet to see Miller.
As far as acting the character, it's Cumberbatch far above Downey I have to say. You really get the sense of his abilities as well as his shortcomings as being who Holmes is. Once again, though, the writing behind the Masterpiece series is superior to those of the movies. Though I must say that Cumberbatch reminds of Brett somewhat. That arrogance that Brett exuded as Holmes. But Cumberbatch brings something else. Hard to describe.
Personally, I've always liked Basil Rathbone as well. There's some old films for you. As far as Watson's go.........Freeman all the way.