And Ellie had the most successful album of 2014 in the UK (with an album released in 2012!), and Burn went top ten/fifteen in like every country, global
Overall? It's tough to say. Ke$ha has had some massive hits (particularly Tik Tok) but Ellie on the other hand has had consistently moderate-successful hits and a stable image.
Ke$ha has had more impact but a lot the attention she gets is negative.