British crime fiction novelist Mark Billingham (Sleepyhead, Scaredy Cat) picks his Top 10 Fictional Detectives for the Guardian Unlimited. It's a strong list, including the likes of Sherlock Holmes, Harry Bosch, Matt Scudder and Dave Robicheaux. (Thanks to Sarah for the link.)
 
One choice that I found particularly interesting was his selection of Sam Spade over Phillip Marlowe. Billingham writes that "I've always slightly preferred Spade to Marlowe, probably just because I thought Hammett was cooler than Chandler."
 
It's likely a minority opinion in the crime fiction community, but one I happen to agree with.  As much as I like Chandler, I always thought Hammett was a little better.
 
I'm surprised he didn't include Robert B. Parker's Spenser, though.  It seems that any list of top detectives would have to include him, even though in recent years he has seemed rather dispensable.