OMG, I love Street Spirit, and Thom's voice is great in that song, but in general I feel that he sings on every Radiohead song the same way, and I really like their music. But Bono's singing is so much more versatile. He may not have the best of voices, but he sings with a passion that you don't find in many other singers. Technically, there are far more better singers than him, but his voice is just so unique. This is really something great in a time where most voices sound very alike.
And Freddie Mercury, that's a whole different level. There will be no one like him again.