Love Britney but she hasn't sung live in 7/8 years. (TRL/SNL Everytime). Rihanna/Katy/Kesha? Oh please.
P!nk is awesome. She rarely has an off-performance. Kelly Clarkson is AMAZING too. Her voice is so angelic, and she doesn't over-sing/scream like Christina A.
Even though I'm not a fan, Beyonce is also a rare gift. The way she belts out those notes is epic, and she does it so effortlessly.