I think Bono incredbile voice first appeard on Tomorrow, just listen to the live versions of that song.
UF
But the album that had most impressing vocals was UF, Uf is far better then JT/R&H. ASOH is like he just discoverd his new voice and just plays with it. Pride, Bad, UF, Wire are all incredible songs in vocal performences. Wire, Pride and UF have never been live as good as the studio versions in vocals.
JT
JT was also a great one, but Bono had lost a bit of the energy and had trouble to hit the notes he did on the UF period, instead he overstrained/scream to hit them(Wide Awake for an example). WOWY is a great one, RHMT, ISHFWILF. But JT dosnt have the energy voice that UF has.
LT
On this tour the energy was back, but this tour inst the best tour in notes. But in scream it is amazing. He had a little tired, hoarse sound in the background of his voice wich was a evidence that this singing isnt good for your voice. Also the falsetto started to appear.
ZooTV
Bonos voice had mature alot since LT, but also where a bit lower. You could realy hear that the LT had done some damage. But the falsetto was incredible and he still had some real power.
1994-96
An amazing voice period, he still had real power in his voice but also had a bit the later voice sound that he was going to have later.
2003
This year is intressting, Bono was very shaky but showed power on NAD and THTBA. It was like he had discovered new power with his voice but didnt now how to use it.
2004
Here he seemed to figure out how to use it...
2005
High C on alot of Wide Awakes, havent hit them like this since UF/COH tour. Miss Sarajevo...
come back later, must drive to my work