I could have picked a whole host of albums to showcase the talents of this woman. I fell for her at the Isle of Wight Festival in 1970 – she played in the midday slot while the French anarchists and the ‘music should be free’ drug wrecks were trying to destroy the festival. She burst into tears and begged for a chance to sing her songs while idiots tried to mess everything up.
That said, at that time she was a bit ‘screechy’ for me in a folk music kind of way, but over the years she became a truly superb writer. With reservations I offer this as maybe her finest hour, though for further listening you may like to consider the albums Blue, For the Roses, Court & Spark, and the slightly jazzier The Hissing of Summer Lawns.
There are lyrics within this album that take my breath away.
The Idle Woman 
I can very much relate to the difficulties of which album by Joni Mitchell to select, all the more so as I also like her early, more traditionally folky albums (“screechy”? no way!) which I think are generally somewhat underrated. What always struck me about her best songs is how infitinely re-listenable they are – there’s always something new to discover, some detail you didn’t notice before, the songs seem almost fractal that way.