answering my own question, i would say that
1. the song everyone loves and nobody hates: We Will Rock You.
i cannot think of any human being that can *not* like this song. Somebody To Love is a better song in the sense that it's more moving, but nobody, no-one does not like We Will Rock You.
2. the most influential: Drive My Car.
i know you're probably thinking "wut?" right now; but when Rubber Soul came out, the N.1 music act in america, The Beach Boys, were ready to release Pet Sounds, they listened to Rubber Soul and said "oh my god, we are shit" and proceeded to re-record the entire album.
Anyway, the Beatles were one of those bands that changed way things *other* bands did. But so did Elvis. You can argue that Elvis was just Blues music, but Rock is a product based on image as much as it is on music; nothing shocking here, films are the same, theater too, almost all art is multi-media. We're not gonna have Arnold Schoenberg here because, while his work may be highly advanced from a purely technical point of view, it fails miserably at being the type of consumable product that Rock is.
3. the most popular: White Christmas by Bing Cosby.
Not really a point of argument; 50 million copies sold.
i should probably point of that, while i have liked, briefly, Bob Dylan, i've since lost a lot of respect for the man (whom i also saw live in the worst concert performance i have ever attended). He gained notoriety mostly for being a turncoat, from folk artist to rock artist, when rock was looking for legitimacy (being branded "degenerate" otherwise) and folk represented the fight between crass commercialism and good, honest values. We all know who won that fight.
And he's also a piece of shit, but that's just him being who he is.
As for Dylan being a poet, so is Arlo Guthrie. Or Tom Petty. or any of the Travelling Wilburys.
4. the most musically important: Little Wing.
Or you could say Johnny B Goode. Or any other song that changed the way other musicians wrote their own songs. The difference with Little Wing is how much it raised the bar. If you look at all rock music of the 50s, 60s and 70, *including* Johnny B Goode, the level of technical skill is pretty darn low. Little Wing - which is today a standard of guitar technique - is unparalleled at the time of release with how much more complex it is compared to anything that preceded it. Two similar examples that will come along later on are Eruption and the guitar work on Master Of Puppets.
5. the guitar solo on Deep Purple's 1972 Machine Head song Highway Star.
I have never felt that Led Zeppelin were important. Ok ok calm your tits.
Sure they were famous. Zeppelin were well known as a great "live band", because they had a great crew and they lugged around a whole bunch of really big amplifiers and they sounded loud and clear.
Keep in mind that until 1968's Altamont's Rolling Stones concert, there were no barriers between the artists and the crowd. Some concerts did not even have proper podiums. Outdoors amplification was not great because a lot of the artists of the time were not cruel businessmen are didn't really think in such terms as image or profitability - they just, you know, did their thing, man, for freedom.
Deep Purple were a *much* better rock band than Zeppelin ever were. Ian Gillian's voice is waaaay better than Plant's (did robert plant get to sing Jesus Christ Superstar? i think not)
They just were shit at promoting themselves and keeping the band together. Also, Blackmore sucks balls live (that's a technical term, look it up).
So if you really want to look at where Rock stopped being Rock & Roll and perfected itself into "Rock", it's probably here.
i think, at some point in the future, when i am old, or dead, y'all finally come around and realize of how great, musically, The Pixies were. I can think of no "better band" than The Pixies. The songs written by Frank Black are those of a man who has learned all the rules of music, and is breaking them.