to be honest, really powerful/memorable vocalists have the strongest influence on whether or not I'll like a band or artist. here are my favourites:
Geoff Rickly (Thursday)
the most beautiful
John K. Samson (The Weakerthans)
I'd want him to read to me before bed
Sue Tompkins (Life Without Buildings)
my favourite rappers really stand out. like, you totally recognize their voice...
...the second you hear it