Wow this is an impossible thread because the Mac has so many underrated songs. Just every song on Tusk is underrated. The entire Mirage album is underrated. Even worse, many Christine McVie songs are underrated especially prior to Buckingham/Nicks.
Say You Will is also full of underrated songs. Too many to list.
I cant think of an overrated song because I don't think the Mac was an overrated band. They earned success the hard way and then surprised everyone with Tusk. For a song to be overrated it has to be successful commercially where everyone knows it.
I would say the song Tusk is overrated. Its a great jam but not much of a song. It was commercially successful but only because it was the first single on a new album after Rumours. I don't think it would have charted if it was the 3rd single release. Its a good song and I enjoy it live but definitely overrated IMHO.
I forced myself to pick one so don't yell at me. I could not come up with an underrated song so forced my hand on this one.