Both Agnetha and Frida have hard core fans, and this is not about making Agnetha the best in ABBA, but an argument between her and Frida. If the argument is based on the information presented in documentaries, books and articles, without question Agnetha was/is more talented than Frida. Denying this means to refute and dismiss reality.
ABBA reached international success because all 4 members clicked perfectly together, but as individuals they were not equally successful and Frida was the least successful. Even Palm wrote that when ABBA formed, Agnetha was the one with the most to lose, because she was already successful on her own. Frida was demoralized before she met Benny. Her success is tied to him and ABBA. Agnetha's did not depend on anyone but herself.