There are no songs on either UEDS or Psychédélices that I don't like in the sense of finding them unpleasant to listen to. Even L'effet is growing on me. I guess if I had to pick one as "least favorite" from UEDS it would be La Candida, but that may just be because it's the only song that I can't understand the lyrics.
I like all the songs on the old albums, too. I even like Abracadabra, although I have to admit that a squalling cat as a musical instrument doesn't work as well as Laurent might have hoped.