In terms of vocal ability, Brad Delp is clearly number one, he is ridiculous. try singing just about anything by boston, good luck, i would recommend ear plugs. Don Henley is number 2 because of his ability to control his voice and the blend of smooth singing and an urgent sounding texture you can only get from 20 years of smoking. listen to the hell freezes over album, this is his best work, last resort, hotel california, wasted time, and heart of the matter especially, oh and desperado of course. after that, steve perry, steve walsh, bono, paul mccartney, eric clapton, billy joel, robert plant(not a great technical voice and mostly falsetto but one of the coolest sounds out there), and bob seger(again a rough voice but great tones and great range) Roger daltry deserves mention as well, along with elton john, glenn frey, and the guy from bad company.