To find the respondent with the best score in the shortest time you can use the Responses List. Just click the title 'Score' once at the top of the page and your responses will be sorted in descending order, showing you the best score at the top.
Here is a guide to How do I find the response with the top score and lowest time taken:
https://www.quiz-maker.com/Quiz-Help/FAQ-Find-Top-Score