Christina Aguilera, in the studio, is miles ahead of any other vocalist around imo.
That said, I find her live performances to be very hit and miss, when she nails it, its amazing, when she messes up its a car wreck.
In terms of live performances, I'd say Beyonce and Leona Lewis are stronger, Beyonce for her ability to change up her songs live and Leona because she is pretty much pitch perfect and I find myself looking for mistakes just so I can tell whether or not she's miming. I think both are potentially as good as Christina, just neither of them really push themselves the way she does.
Not particularly blown away by any guys at the minute.
Seriously, what part of
this century do some of you not understand?