I'm going to put Casino here. On it's own the film has had positive reception but it is overlooked in favour of Scorsese's other crime film Goodfellas. Now, I'm not saying Goodfellas is bad (it's great) but it is overrated - the protagonists become unlikeable later on in the film and nothing seems to happen for long periods of time. If I'm honest, I found myself just wishing the film to end after about 2hrs.
On the other hand, Casino features a protagonist that we root for pretty much all the way - he is kind of being screwed over by the different forces around him but still maintains his cool most of the time and doesn't go off the rails. If you enjoyed the camerawork in Goodfellas, it is bigger and better here, with some marvellous shots of the casino and the tables as the camera pans over and around them. The acting is equally as good, the plot is IMO tighter and easier to follow, and, well, it just seems to me that not enough people have seen it, yet they'll compare Goodfellas to it nonetheless, which pisses me off.
Barry Lyndon, although I only say that now because every time I mention it to people they seem to have absolutely no idea of what I'm talking about! It's a quiet little film and I imagine that it's not for everyone but it has some of the most incredible imagery you'll ever see on film. I heard someone describe it as the work of a genius who is very bored.
My votes go to Jiro Dreams of Sushi