This character opposition is one of noir's innovations, I think. The novice or amateur criminal bumps up against some variation of criminal, in the range of "ruthless" to "psychopath." It actually stems from a certain strain of classical comedy (and by "classical" I'm referring to all the way back to Elizabethan times) where the heroine is courted by two flawed suitors who are differentiated by various forms of temperament.

A great example in "classic" noir is Christian-Jaque's VOYAGE SANS ESPOIR (1943), which pits ethereally handsome novice Jean Marais vs. the prison-hardened, ruthless, darkly menacing Paul Bernard, whose charisma is measured in units of danger.

What later films do to keep us "interested" is to add more flamboyant flaws to both characters and try to layer them into the narrative in ways that hide the extra, "over-determined" plot dynamics that were worked out to make the characters' actions seem believable. In the old days, they weren't quite so worried about all that, since a significantly smaller percentage of the viewing audience was already that jaded...