some weeks ago i read an article based on stats from the last 8-10 years, and ben yedder was on the top of the leaderboard in conversion rate, with cavani and aubameyang completing the top3. costa, messi, lewa, lacazette and icardi also made it to the top10.
i'd also say that both van nistelrooy and makaay must be on an all-time top10 list, they were deadly back in their days. my father used to say that gerd müller scored from most of his chances, he's a safe bet too. i watched a lot of vintage footie, both kocsis and puskás scored a lot without missing too much. but since detailed shooting stats are unavailable for the majority of football history, it's hard to pick anybody based on facts.