First of all, Clapton shouldn't even be considered a peer of the other two. The only (male) peers to Dylan and Cohen are perhaps Tom Waits, Johnny Cash, Van Morrison, and Neil Young.
*first: I love early Cohen. I don't like late Cohen. And while I've only recently started to listen to him, I enjoy Dylan more every day*
As for Cohen, his music is powerful, and more complicated than Dylan's. He really stretches the boundaries of keys, and phrasing of melodies. His lyrics are more poetic in the traditional poetic sense... imagery, diction, rhythm, etc. He was a poet first, after all. His guitar skills are comparable with Dylan's, and while his voice was better, it's now probably just as bad (according to the normal standards of what makes a singing voice good) as Dylan's.
Dylan's music is just as powerful, yet simpler... that doesn't mean it isn't as good, however. His lyrics are poetic as well, but in a different sense. He's more metaphorical, and better suited to ballads... telling stories. His lyrics represented the time and the feelings of his generation, while Cohen's lyrics were more personal or obscure. Guitar skills are average, and that voice is a little sketchy, although at times was no worse than Corgan or Cohen.
The bottom line is Dylan is more prolific (more songs, more albums, longer career) and has had a greater influence (on musicians, on songwriting, on lyricists, on people). Cohen is for those who love deep lyrics, and interesting songs... usually the more discerning music listeners / artist types. But Dylan is for everybody... from the highbrow critics and artists to the average listener who loves Like A Rolling Stone and All Along The Watchtower.
I know that Cohen really enjoys Dylan, Morrison and Waits. He'd probably tell you that Dylan is better than him.