A harder question than it sounds, as my initial inclination would be to choose one from the top tier of possibilities that I had read most recently. But, after a little thought, there's really only one choice for me.
Hmmm...Harry Dresden? Yeah, I guess I can roll with Harry, although I think of him more in terms of fantasy. Same with the wonderful Anita Blake, before Hamilton started succumbing more to romance than action and mystery.
Right now I'm reading through the Poirot novels, and of course, Holmes is always a fallback. However, I will pick Mr. Bond as the ultimate hero. Yeah, trite, I guess. But come on, it's Bond, James Bond.
And if we talk about villains...it's Lecter, Hannibal Lecter
But let's not forget Rex Stout's Archie Goodwin. A smart-ass with charm. Or there's Tony Hillerman's Jim Chee. Or Ed McBain's Steve Carella. Or. . . and I'll make no apologies for this. . . Earl Derr Biggers' Charlie Chan.
Of course I'd put Phillip Marlowe right up there with the best of'em. But the early, early Perry Mason novels had Mason with a suave mean-streak in him. I liked that.