I dunno, it keeps changing 4 me all the times..the one moment i think that a female or a male singer for that matter sounds okay...they do a disappointing performance, or worse still do a cover of a song and it's a real fuck up...
but, one name that comes to mind for me is Toni Braxton. The depth and the quality of her voice is not bad, in my opinion and furthermore, i saw a playback of a live performance of hers and she could sing live...and for me, that is really important...If a person cannot sing without the backup of voice altering stuff...than to me, that singer can't sing too well - maybe they're just having a bad day!