Every decade has got some brilliant examples but if I have to pick a decade then I will pick two. The two best decades are the 1920's and the 1950's.
The 1910's were all about getting the technology right, so by the 1920's, the tech problems had been sorted and it was before the censorship of the early 30's curtailed the depth of a story that could be told. In the 30's to early 40's, sophisticated entertainment using the new color process, was often more important than the story.
Post war and into the 50's, directors, writers and actors were boldly prepared to challenge the stereotypes and provide a new perspective to the stories they told. The 60's and into the '70's were a polished bunch of films that showcased the best of what had gone on before them. The modern era of film probably begins with Star Wars in the 70's, since then through the 80's, 90's, 00's, and 2010's the medium of the story has possibly become more important than the story itself. The sound, 3d, digital stock, effects - models and cgi, now create the entertainment more than a good story.
When the technology is sorted out, it will be another generation that will produce the next crop of really good films. Maybe in 10 or 20 years from now and not led by Hollywood.