It isn't really a contest. Although I still consider Jeremy Brett's Holmes to be definitive, I get a kick out of Benedict Cumberbatch's interpretation (still, I mostly watch Sherlock for Martin Freeman).
But I actually like Jonny Lee Miller's Holmes.
In many ways, Miller's interpretation is closer to Brett's than Cumberbatch's. His Holmes is less austere than Brett's (although the drug issue is just as strongly referenced, more so than in Sherlock). More importantly, he exudes Brett's kindliness.
Visually, he isn't as tall as either Brett or Cumberbatch, being more compact (a build that I find enormously attractive). On paper, Sherlock Holmes is supposed to be tall and lanky, yet I rarely notice Miller's height either way, possibly because of how he carries himself--and also possibly because he is paired with the exceptionally petite Lucy Liu (who looks tiny even in heels).
It makes him a far more relatable Holmes--yet, I don't find the interpretation too sweet or cozy. Miller's Holmes is a real (brilliant) guy who might actually be more than just Mr. Supersmart Detective someday.
I can only hope the solution isn't a series of "other" relationships. So far, the writers have relied instead on the characters' "roles." Holmes and Watson relate initially as client-therapist followed by employer-employee; consequently, the characters themselves don't seem to realize the part attraction plays in their relationship. Since Miller's Holmes is clearly smitten with Liu's Watson--and just as clearly clueless to the fact--this is just as well.
It's possible that the writers will employ the Scully-Mulder solution: ignore the possibility of romance until it becomes absolutely necessary. And I must say: Miller-Liu are the closest thing I've seen to Duchovny-Anderson in a very long time.