Holmes is literature's greatest autistic character, I think.  He obsessed about cigarette ash, handwriting, the way objects would wear and erode, everything but people themselves.  I'm not an expert in the series, but I don't remember Holmes ever solving a case by sussing out the motivations of the other characters.  It was always through his clever deductions based on forensic evidence that he was able to whittle down the culprit.  Watson was the only person he could really relate to, which is why it was so important to have him along on the cases.

That's why I'd like to see Ewan MacGregor do the part.  I don't know if it's rigorous martial arts practice, rigorous acting training, or just the way he is, but he has this air of incredible self-control on screen.  Every movement he makes is extremely fluid and precise.  The effect makes him great as a Jedi, but a little weird to watch when he takes the role of a mere mortal.  This kind of disconnect could work well as Holmes.

You can find some classic Holmes movies, including Dressed to Kill with Basil Rathbone, in the public domain at the Internet Archive.

(is 3fingerspointback)

Jeremy Brett captured Holmes' manic energy, something that usually gets left out.

I would like to see Rowan Atkinson portray Holmes, with that guy who played Baldric as Watson.

I'd have to go with Nicol Williamson in "The Seven-Per-Cent Solution"...

Basically because his version of Holmes was the one I grew up with watching old Holmes movies on the tube.  But I have to put a vote in for a really unconventional and dynamite version of Holmes released in the 70s.  The Seven-Percent Solution featured British actor Nicol Williamson as Holmes and Robert DuVall as Watson.  The cast also included Alan Arkin, Vanessa Redgrave, and Sir Laurence Olivier.  The plot includes Holmes being treated by Dr. Sigmund Freud for drug addiction while he matches wits with Dr. Moriarty.  Definitely a big recommendation to include to your Netflix queue.

Illegitimi non carborundum.

Now that he's getting a little long in the tooth and has been dumped from the Bond franchise, wouldn't Pierce Brosnan make a decent Holmes? He's got the accent and he's got some pretty decent acting chops. I think it'd be a good fit...

Ah, one of my favorite books as a kid and favorite movies, The Hound of the Baskervilles, with Basil Rathbone and Nigel Bruce.  

There has never been another "Sherlock", AFAIC.  It's like Sean Connery as "James Bond".  None of the later ones were ever in the same league.

there's only one way to find out...

    While I'm not very familiar with Rathbone, after a few moments poking around on Youtube, I can see why he's considered the "definitive" edition. In repose, he looks very much like the drawings, and unlike Brett, Rathbone doesn't run his mouth very much-- Brett plays Holmes as more than a bit of a chatterbox, but that may go with the stories selected for the series. (More on that later.)
    I guess the biggest difference for this viewer, and a game breaker, is the portrayal of Watson. Nigel Bruce, as I recall, and as verified by said follow up, really played the doctor as a blunderer, a buffoon even. You have to wonder, after a while, why it was Holmes kept the guy around, even if he was saving the cases for posterity. (You also wonder if any patients ever came back for a second visit, eh?) This is never an issue with the Granada series; Hardwicke and Burke (one of them, anyway) have stated that they played Watson as a man of ordinary intellect who just happens to be in the presence of a genius. The only comic aspect to Watson I can recall is the way he's always thinking of where to eat and sleep next-- but I understand this is a trait shared by many soldiers, ex- or otherwise.
    What's also endearing about the Granada series, and this isn't all related to Jeremy Brett, is the way the faithfulness to the stories allow Arthur Conan Doyle to stand out with all his defects. As Raymond Chandler pointed out in The Simple Art Of Murder, Doyle made mistakes that totally invalidated the stories, but that it didn't matter. (And if anyone thinks that would make a good review/sub, send me a PM and I'll poke around the Net a bit.) In one story ("The Dancing Men"), Holmes finds the ejected cartridge of a revolver(!); in "The Speckled Band", the snake is supposed to respond to a whistle, even though snakes are pretty much deaf; and so on.
    Even more interesting is how insular, even how cozy they are: preventing a lady from entering a "bad" marriage (usually to a foreigner), or saving an ancestral home from foreclosure, or some other disturbance of domestic bliss. This is where the "chatty" Holmes comes across so much better; it's hard to see Rathbone accepting a commission to find out the goods on an older woman who drove a younger man to suicide. (Seriously. The story is "The Three Gables") Doyle wrote the stories, Brett and the rest just did what they could with the words . . .
    So while Rathbone deserves his crown as the definitive Holmes, I have to side with Brett when everything else is considered. Even down to the top hat over the deerstalker-- you really get the sense of Holmes as a city dweller, and not just the guy in the funky hat :)

Ex ignorantia ad sapientiam; e luce ad tenebras

The best Sherlock is Data.

It's the end of the world as we know it, and I feel fine