BoA... she is one of best dancers i ever saw on pop music...
Namie choreographies are not that impressive, and her dancers always outdance her...
The same goes for Koda Kumi...
Jolin is still learning...
I don't know Nami Tamaki
Hitomi Shimatani is as good at dancing as Ayu (what doesn't mean much)
Even if I'm not a BoA fan, none of the others in the list (or even Britney as someone said) are able to do this:
http://www.youtube.com/watch?v=McJ-dwtbWC8
or this:
http://www.youtube.com/watch?v=2gqncPEjw2Y