We all know Madonna is the best selling female artist but how long will that last, Rihanna is the best selling female singles artist in the UK, I think she now has more cumulative weeks in the charts and she's also got about 6 million selling singles and Madonna has none.   Rihanna also has more number 1 singles than Madonna in some countries including the US and I reckon it won't be long until Rihanna has more number ones than Madonna everywhere and becomes the biggest selling female