Fair point, Jenn...no you didn't misunderstand me, I'd forgotten that I'd listed MY favourite singers originally - so you were quite right to list yours!
I'd agree that mentioning people you dislike (however distinct) would be hard to do, although there are some really distinctive voices around today who just don't grab me at all. Look at Eddie Vedder - his voice seems to polarise people: we either seem to hate it or love it - no in-betweens. Personally I can't stand him, and not a big fan of either of the Finn brothers' singing voices (Shock! Horror!). Although their voices seem to FIT their songs in the way that other people's wouldn't...sorry if I'm confusing you.....
I think it's all very subjective...if you like an artist's music you're much more likely to think that they are distinctive.
So I accept your comments completely!