For me (and this is of course personal) two stand out as perfect in execution:
The Fifth Element
Crouching Tiger Hidden Dragon
Up, whilst excellent and moving, isn’t perfect. The pathos of the beginning takes a back seat whilst a kids’ movie takes over. Not that kids movies are bad but the change of tack gets it marked down *very slightly*
We are talking about perfect films, not films you really liked. You can love a flim that has flaws. Taxi (French) for example is hugely enjoyable but not a perfect film.