Owen Wilson and Jennifer Aniston lived in their characters. Can not imagine anyone else could have done better. Marley & Me, though the story does not have the usual thrills and frills, directed so beautifully and sums up the life of a family member, in this case a pet.
The conclusion of the movie with this dialogue
"A dog doesn't care if you're rich or poor, educated or illiterate, clever or dull. Give him your heart and he will give you his"
is just awesome. This movie makes it to the list of all time classics and an eternal movie.