I think the best you could ay is that Axl is unique. I mean no one would ever call Udo a great singer.
Axl is in the same range of 'unique' that also has Dave Mustaine, Dylan and early Geddy Lee. They're all singers of 'questionable' skill, in fact, I'd say that Axl is number 2 on that list, right behind Geddy.
Voted GnR even though Boston is pretty great too but I just get more joy outta GnR.