I've read in few papers that elliptical winglets give better performance than blended in terms of their L/D ratio. I am not able to find why elliptical winglets are better. the two differ by their profile followed. Edit 1: Here are few references http://ijari.org/CurrentIssue/2017Volume4/IJARI-ME-17-12-148.pdf
Edit 2: The papers explain that elliptical winglets are better than blended just through observations from CFD study.But they do not draw conclusions on how it is better and I couldn't understand that from the contours also.