I genuinely don't know if I have a preference for vocal style, mainly because my musical taste is
all over the place. Sometimes it's hard to separate the instruments from the vocals in what I like about a particular song (or even band), too.
Just going to throw some out there based solely on my preference for vocals, see if they group together at all:
Florence (and the Machine)
The Cranberries
Garbage
(okay I'm seeing a specific trend there already, but bear with me - Garbage is a pretty recent hook of mine, so that skews my listening preferences a bit)
The Pretty Reckless
Halestorm
Red Hot Chili Peppers (vocals-wise, the more mournful stuff like Otherside and generally the By The Way album, me thinking Kiedis is a dirtbag aside)
Meatloaf
Foo Fighters (more than Nirvana, definitely prefer Grohl's range to Cobain's, as sacrilegious as that might be

)
Some other scattered bits and pieces, like I love this cover by Gerard Way:
Those are probably the bands where the vocals resonate best with me, there's a ton more music out there I like for their instrumental qualities, or just because I need a specific genre of music at the time.