I like okay singers a lot. This is not to say I dislike great singers--David Bowie, Peter Gabriel and Maynard James Keenan are at the top of my list for male vocalists--nor that I like straight up bad singers--Ian Curtis' voice will never win me over no matter how many times I hear "Love Will Tear Us Apart." However I do greatly appreciate frontmen who may not be the best on a technical level and yet manage to rise above their limitations in a holistic fashion.
None of the guys in Pink Floyd were particularly good singers, though David Gilmour's scratchy vocals did a fair job most of the time. But in terms of sheer versatility bassist/chief songwriter Roger Waters and still is incomparable. In the course of The Wall--Hell, in the course of its climactic song "The Trial"--Waters adopts six distinct character voices. It would be a nerdy '70s prog rock/rock opera thing to get excited over were it not for the fact that he's a genuinely underrated voice actor. Gilmour's choruses on "Comfortably Numb" may be the best vocals ever on a Pink Floyd tune, but in the grand scheme of things Waters' contributions had more personality and were consequently more immersive.
Oh Win Butler. You constantly sound hoarse as all Hell and you have trouble staying on key in a live setting but I'll be damned if that isn't representative of Arcade Fire as a whole: clumsy but endearing and oftentimes transcendent, be it his desperate wailing in the climactic portion of "My Body is a Cage" or the comparative restraint of "Suburban War". He's definitely a student of the David Byrne school of singing, which as explained above isn't a bad thing by any means.
And then we get to that Gollum of a man, Thom Yorke. God, I love him. I don't care how shrill he can get, or how whiny, or how muddled his lyrics become in the process, because his voice has more character than maybe 75% of mainstream singers I've heard in my life. I won't indulge in superlatives. Just listen to "Pyramid Song", "How to Disappear Completely" and "Codex" and enjoy.
An aside: In the first paragraph I made sure to note male vocalists because, as this list reveals, I don't think I appreciate female vocals in the same way. I'm not deliberately applying some double standard ("The guys are allowed to half-ass it but you better get your shit together, girls!"), it's just a pattern I noticed after the fact. Though have noticed a couple of exceptions, namely Amanda Palmer.