From those performances you linked:
1. J'ai Pas Vingt Ans
I like how energetic the choreography is compared to that of the other performances linked. I also think that dress looks perfect on her and it's one of my favorite songs of hers.
2. A Contre-Courant
Also one of my favorite songs of hers and I like the way she dressed when performing ACC, specially that outfit. There's also a certain warmness in her eyes every time she performed that song on TV.
3. Mademoiselle Juliette
I don't like the song that much, but that performance was great and I think that from 2007 to until the Blonde album was the peak of her beauty.
I, of course, still think that she's beautiful, it's just that she doesn't perform live that much anymore (understandably so). She has a certain charm when she's performing or doing anything on camera (even just talking), that traps you.
4. Parler Tout Bas
My favorite song on hers, because I think her voice is beautifully perfect for slow ballads. That one and Amélie m'a dit are in my top 5 songs that put me to sleep
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I don't have much to say about the performance, but her constant smiling is enough to put it on the fourth place.
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Never liked J'en Ai Marre nor Moi Lolita, but I prefer the En Concert perfomance for JAM and the Tubes D'un Jour performance in 2003 for ML.
Even though L'alize and Gourmandises are one of the songs I like the most, I don't like those perfomances that much, dunno why, maybe it's the short hair. I think I prefer the En Concert performances and, specially, her live voice for those songs.