To think about definitive versions of jazz standards is tricky, mostly because it's quite subjective. But the fact remains that there are certain artists who are considered touchstones, and their performances are the ones that are most frequently consulted by musicians and serious listeners who want to try to understand the essence of a song. Among instrumentalists, one name that is brought up in this regard more than any other is the pianist Bill Evans, for the simple reason that his musical approach is deeply grounded in fundamentals and therefore contains no wrong turns. As Cannonball Adderley said, on the cover of 1958's Everybody Digs Bill Evans (the quote-filled sleeve was the record company's idea; Evans, who was a modest person, didn't like it): "Bill Evans has rare originality and taste and the even rarer ability to make his conception of a number seem the definitive way to play it."

Here's a version of "What Is This Thing Called Love?" that exemplifies that statement: http://www.youtube.com/watch?v=yY82ZNEgNHY.