If film viewing is wrong, I don't wanna be right
Shannon's question (who is the better on-screen Sherlock Holmes: Basil Rathbone or Jeremy Brett?) may prove controversial, but here's my vote: Jeremy Brett.
Rathbone's portrayal is intriguing and suggestive of hidden depths, but Brett's depiction offers even more of the arbitrariness (sometimes downright hostility) that hints at smoldering emotions and something repressed.
On a scale of 1-10 in casting appropriateness (1 is "disastrous", e.g., Leslie Howard as Ashley Wilkes in Gone with the Wind"; 10 is "ideal", e.g., Colin Firth as Mr. Darcy in Pride and Prejudice or Zachary Quinto as young Spock in Star Trek), I rate Basil Rathbone an 8 as Sherlock Holmes, compared to Jeremy Brett's 9. The Holmes character is so difficult that both ratings are sincere compliments; a 10 may not be possible. There, those opinions should stir up an argument or two!
At least we can agree that enjoying movies doesn't hinder our literacy and doesn't constitute cheating on the books. I have finally gotten past feeling unprofessional whenever a great novel-related movie comes to mind and I'm compelled to mention it. Surely it's OK to share that, for example, Gillian Anderson was wonderful as Lily Bart in The House of Mirth, or that Balzac and the Little Chinese Seamstress is available on DVD. After all, who's to say which literary format speaks more eloquently to the individual?