I think on a song by song basis, the overall quality of Tango is every bit as good as Rumours. As an album, it's cohesive, flows extremely well, and the album as a whole tells a story. I think Tango is the last really great studio album Fleetwood Mac released.
Mirage on the other hand is a lot more jagged. There are songs on Mirage which are far superior to almost any Mac songs of any era (Gypsy, Hold Me, Eyes of the World); but as an album, Mirage is not so great. The song quality is so highly varied, the majority of Lindsey's songs seem like snarky afterthoughts, and there is no real cohesive theme bridging the 3 songwriters.
I've always felt the extreme turmoil brewing during the making of Tango (which I argue was probably even worse than the Rumours turmoil) fueled incredible music. On the other hand, you can practically hear how disinterested the band is on Mirage... they seem to be just going through the motions so they can get back to focusing on their solo efforts.
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