Wow, what an interesting question. And I never knew it was so commonly discussed.
I'm a U2 fan. I do like Queen quite a bit, and I know a fair number of their songs, but I haven't studied them. I'm not clear on the chronology and I can't speak to how Freddy's voice sounded live.
That said, I've always assumed Freddy had the better voice. He does have a higher range, and his voice is clearer. I've heard Bono miss notes, maybe Freddy did too but I haven't studied him. Made in Heaven is a jaw-dropping vocal performance, and he made it seem effortless. He was obviously quite the showman too. And I did love his style very much.
Still, Bono's my guy. I do hear more of a range in vocal emotion from him - not to say at all that Freddy was stunted in that department though. Bono's type of showmanship just appeals to me like nobody else. Freddy had a gorgeous voice, but he can't soothe me like Bono can.