Christina Aguilera.
Her voice is more versitle. Yes she screams and stuff on SOME records, but she can go from
to
to
Meanwhile I think Kelly, whom I love to bits, kinda sounds the same inmost of her songs.
This. I prefer a more signature, unique voice personally. You want true vocal precision and talent, you don't look at the commercial pop lists. Xtina's voice disputably differentiates her from a crowd more than Kelly's. She's more than proven her versatility, range and ability to control her voice. She's less predictable, as you can clearly see by the videos Darius posted. That raw, vocal straining, tone and ad libs DEFINE her... but from one video to the next she can suddenly change everything up - she consciously decides to sing in that "messy" way. Yes, it's very imprecise and messy to the trained, anal ear. Now, do those people constitute the majority of commercial pop audience? No. If all I appreciated were flawless vocalist, commercial pop would be one of the last places to look.
I'm not such a big fan of Kelly because she makes it sound easy. She's great, effortless and has a super clean, crisp voice. Lots of people on the radio have this already. That isn't going to make me go out of my way to see her in a concert. I want to hear blood, tears and real emotion in a voice. Example. I love Usher. You know how many people can replicate Usher's voice? Does that increase his value as an artist? How many less-successful Ushers are running around? If he wasn't such an amazing dancer, I wonder how successful he'd be. The real interesting voices sound like an absolute DISASTER when people try to copy them. That's what I enjoy paying money for. That's why Xtina > Kelly. Although Kelly is awesome too.