I can’t really tell, because there were, like in any
other Pixar-movie, so MANY good scenes.
But I have a few I liked a little more better:
The Opening scene -
Best opening scene from a pixar-movie! Whoohoo!!!
The Final scene - oooh, so amazing!!!
Tractor-tipping
and Pit Stop Final - the funniest scenes !! 
The end credits - What I laughed in the theatre.
The
touching scenes like the goodbye-scene or the Doc-scenes were also great!