RHCP is also one of my most favorite bands - ever.
I'll go with your #3 pick. It's rare and not well known, and it's a pretty good song. But, I can't agree with your top 2 picks.
"Soul To Squeeze" is a great song and a great video. It got plenty of play & recognition in its' time for the great video and its' inclusion as the main song in the Coneheads movie. All around, I think this was a very popular song in its' day.
ANY SONG off of BloodSugarSexMagic could never fall into the "underrated" category - because Rolling Stone magazine crowned the RHCP and this album as the most significant band/album of the 1990's. Not to mention, it has sold over 13 million copies. The entire decade of 90's pop culture would have been different without it.
So, for my most "underappreciated" RHCP song, I picked one that actually has been made fun of and ridiculed by music critics. However, it is a song that gets "stuck in my head." The only thing is, if it does, I don't mind it:
Love this one too. I can see what you mean. Guess I just didn't know BSSM was that huge :) I mean I knew it was their breakout album of sorts.