Freddy Mercury and Steve Perry have terribly thin voices. They're good voices, but their range is very limited at best. To be considered with the best, you must have amazing range. As a male vocalist, you must have serious balls but also be able to belt out the highs as well. Al Green, Marvin Gaye, Robert Plant (in his prime), and Van Morrison come to mind, but there are many others. Versatility is another major consideration... being able to single a mellow ballad as well as belting out a powerful song is important when considering the greatest male voice. Come to think of it, Elvis could cover most of these criteria as well, but his voice was a tad thin.