The pinnacle of Stevie's career is her contributions to Tusk, all 5 songs were written to perfection, sung with all of the strengths and weaknesses of her vocal capabilities and never to be matched again. The demos from that era also could easily have interchanged and we'd still have her best set of songs on any Fleetwood Mac album. Now, this is where I'm going to contradict myself and go from my favourite Fleetwood Mac album to discussing Stevie's best work and blow my argument
Back to the perfection that is Rumours. Gold Dust Woman is in my view, her very best self penned recorded song. It fits perfectly into any classic rock set played on the radio or at home, it just does. It is also the only song she has pulled off live at every single concert even on an "off" night, going back to even some of the problematic shows of yesteryear where Stevie could barely talk let alone sing. Someone said earlier how Dreams while being a pop song also recaptures the blues side of the band, and it certainly does. The high notes on that song are also just wonderful and left me longing for more, that was really never to be again (although brief interludes on Sorcerer, New Orleans and Call on Me for Magic). I Don't Want to Know also is her most "forgotten" gem, a flawless song that is so catchy, I still love playing it. The Chain also shows just how good Stevie's songwriting was, despite her limited chord knowledge, she could pump out a killer melody and lyrics that none of her contemporaries would dare touch. The demo of that song left me scratching my head as to why the structure of that song never wove itself into another song, it' stunning. Lastly, there's Silver Springs, again the songwriting is immaculate and the vocals on record, she would not match until 1997 when she hit the song out of the park on the Dance. Fleetwood Mac's greatest misstep was not including this gorgeous song on Rumours and making it the lead single for the album. It's that good.
I agree with the earlier posts about Mirage and Say You Will, each contained some of Stevie's best work and are honourable mentions, but Rumours and Tusk are flawless where the later works have cracks in the armour of what was clearly some of the best material ever recorded by a rock and roll band.
Don't get me started about Tango in the Night as I'd rather forget that one.