It depends:
1. Do you mean who can sing highest - or - do you mean who can sing highest AND lowest....like who has the widest range.
2. Many singers can vocalise notes that they don't sing - like squeeks and cracks and screams in addition to the actual singing range.
Here's the stats from
http://therangeplace.forummotions.comJustin Hawkins: Sung range: B2-E6, Total range: A2-E6
Axl Rose: Sung range: C♯1-A6, Total range: C♯1-C♯7
Bruce Dickinson: Total vocal range: F1-B5 Sung vocal range: E2-B5
Chris Cornel: Sung range: D2-A5, Total range: B1-C6
So when singing it looks like Justin can sing higher than Axl, but Axl has a much wider range of notes as he can sing significantly lower and is only a few notes shy of Justin's top end. Bruce can nearly get as low but no where near as high. Cornel is only just shy of Axl's high notes, and is close to his bottom but not as deep.
So I'd say Axl has the widest of this group, while Justin is the most extreme in terms of highs.
Of course there's also the way they hit the notes too - Axl hits them with an anger and rasp that's pleasing to my ears but not for everyone.I