I think as far as songwriting goes, Edge is just as vital as Bono. I'd imagine it's like most great songwriting duos - they are better together than on their own. As a matter of fact, when I think of U2, I most often think of Bono and Edge, as it seems from interviews that when it comes to really getting out the song structure, most of it falls on Edge and then Bono.
Just a few examples, Edge came up with the genius intro to Streets, he also came up with the majority of Sunday Bloody Sunday (Bono came in and changed the lyrics, of course). Anyway, my point is that great lyrics aren't enough if the melody and structure sucks, and a great melody and song structure is nothing without good lyrics. So I don't particularly view either Bono or Edge as stronger than each other. And in Flanagan's book Adam or Larry (or maybe both, I forget) discuss that if they were to do a split according to who does the most work in the band, then it would probably be in Bono and Edge's favor.
Not to say that Adam and Larry don't pull any weight. I think they're great because Edge and Bono can throw all these weird ideas at them and Adam and Larry can take it all on. And there's no denying that certain songs do seem to be geared more towards the drums and bass.
So to sum all this up, the way I see it, it's Bono and Edge, then Adam and Larry, but they all form a very cohesive unit.
[This message has been edited by Diemen (edited 04-25-2002).]