Can someone recommend a few Joni Michell albums?

One idea is to start at the beginning - Song to a Seagull.  Just Joni and her guitar.  Unfortunately, it's poorly recorded, but - in many ways - it's the most essential record she's made.  Blue, Hejira and Court, and Spark are all great, too.

Indeed Song to a Seagull is wonderful music. Agree with Martykl on the sound quality. We can blame David Crosby for that (-: If forced to live with only 3, I would likely chose Ladies, For the Roses, and Hejira. But I'm glad I get to keep Blue, Seagull, and Court. As much as I like all of these, I am sitting on a sealed copy of Hissing that I haven't opened for years. I can be strange like that.

Just buy the 68-79 box set. You can thank me later.

She really has a great body of work. If we stick we the original question, it's got to be Blue,  then  Court & Spark as two starters.
The passion from so many here on a variety of LPs says much about her depth as an artist. There aren't too many artists who have passionate fans of what others might call her 10th or 11th best album! She is absolutely a benchmark in female vocals, folk, rock & jazz. Cheers,
Spencer

I would take the approach of getting one from the seventies , one from the eighties , 90's .... ect  . then decide which era you like and get more from that era first . Her album Dreamland is sonically incredible .