I think Female mainly since my favourite music is pop music ( I'm fifteen ) and female pop vocalists are much better than males in this type of music.

I like both but the majority of my top artists (on Last.fm) are female or bands with a female singer: Madonna, No Doubt, Metric, P!nk, Lana Del Rey, Florence + the Machine, Yeah Yeah Yeahs, etc...

There was a time when I might have agreed, but now I'm pretty convinced that there's just less they can do with their voice, and their voices sound so similar to one another.  And believe me, I'm not one of those people that says music sucks because of what's on the radio; I like a lot of different music and I do a lot of digging for it.  And every time I think I hear a woman who sounds cool or interesting, it ends up being a guy.  Guys just have more character and individual differences to me.  In my ears most women sound the same.

Of course different people appreciate different things in a voice.  I like uniqueness, but if someone prefers pitch-perfection or inflection or something else they'll feel differently than I do.

(While we're on the subject, Amanda Palmer is one of the few female singers that I really like.  She can get super deep with her voice, and it's awesome.)

I like uniqueness as well, all that really matters to me is how a voice resonates with me emotionally, but I don't really care about how good someone is in a technical sense. Of course sometimes technical ability helps, it's just not something I specifically need.

What kind of stuff (besides Palmer) do you usually listen to?

I am like you. There's off course good female singers, and there are of course good songs that sound good by female singers, but they pale in comparison to the quantity of good male singers. Moreover, I think the very best female singers ever, don't sound as beautiful to my ears than the very best male singers of all time. My iPhone is literally stuffed with music, but I don't have a single female artist on there.

I like both in general, I just can't stand male voice in doujin music and j-pop.

Recently most of the stuff I've been listening to hasn't had a lot of regular old vocals--a lot of electronic music and stuff--but off the top of my head a few of the male vocalists I really like are Damon Albarn (Blur, Gorillaz) and Josh Homme (Queens of the Stone Age).  I also really like Jason Lytle (Grandaddy) and Thom Yorke (Radiohead), though I think I more just like the music and how their voices fit into it than the actual sound of the voices themselves.

female: (some of my fave vocals)
fiona apple
etta james
tori amos
janis joplin
annie lenox
stevie nicks
beth gibbons
carly simon
jewel
joni mitchell
kate bush
tracy chapman

Both, depending. But I actually prefer no vocals. Unless its entirely melody.

Female for power metal.

and Males for thrash metal.

Everything else depends on the songs and the tension

if it's pop? Males sounds like females, and females sounds like Females.

I think we all know that marked is owned by women