I absolutely adore Under My Skin and I feel like that is my favourite album by her. But to be honest I do not feel like she has a big magnum opus that eclipses others. I think I would rank The Best Damn Thing third personally, after Goodbye Lullaby. However I feel like the Best Damn Things is her biggest era and it does host my favourite songs by her. I tried to have all the artist represented by their biggest era, but maybe we should go for her highest average then in that rate. Let me check those averages without bonus tracks cause I think they bring the average up for TBDT and down for UMS.