Likes and dislikes of languages are dreadfully subjective things.

Mostly the criteria people use seems to be phonological (phonaesthetics) or semantic. Grant Barrett ran down the intricacies of the supposed beauty of cellar door in a recent New York Times Magazine Language column (link). For the other, see the various least favorite words discussions (on say Language Log) which include blog, moist, panties, et al.

[Addendum: Geoff Nunberg noodles on Barrett's Selladoa.]

Ceci n'est pas un seing.