I'd like to have my next PC be a pirate who fences stolen goods and who is effective at her job because she can defeat her rivals in direct combat (as opposed to hiding and stabbing them or ruining their reputations). What class would be best for such a concept?
Use the Criminal background, not a class
Instead of focusing on a particular class to play, you can simply select the Criminal background (PHB 129):
You are an experienced criminal with a history of breaking the law. You have spent a lot of time among other criminals and still have contacts within the criminal underworld. You’re far closer than most people to the world of murder, theft, and violence that pervades the underbelly of civilization, and you have survived up to this point by flouting the rules and regulations of society.
This background gives you the skill and tool proficiencies that are relevant to being a criminal, as well as personality traits and features that befit a criminal.
Because backgrounds can apply to any character, you can play as any of the martial classes, given that any of them could defeat an enemy in direct combat.