Hard to beat the caustic and sometimes poetic first person observations of Mr. Marlowe. I like Travis McGee a lot, too--and Grijpstra and De Gier. I always found Holmes insufferable, but that's probably just me.
Travis McGee was great, and so is Dave Robicheaux. I also like the early Spenser novels by Robert B. Parker. He phoned it in for a number of years, but I thought the last few Spenser novels were reminiscent of some of his earlier works.
That's good to hear. I was a Spenser devotee for years, gave up after HUNDRED DOLLAR BABY, using almost your exact term to my wife. (He's just mailing tem in now.) I'll have to pick up one of the more recent efforts.
The Continental Op. Because he's bald and fat. In essence he shouldn't be cool but he is. Sam Spade was cool, mostly because people remember Bogart playing him. Same with Marlowe. But the Op was different. His modern equivalent could be Rebus because he's essentially an unlikeable who's very compelling and likeable purely because he's not a nice person.