imho Icelandic is the very most beautiful (sounding) language.
because of their way of preaspiration of plosives like whispering sometimes and adding the article at the end of the word, the language sounds mythical and epic. I would not be astonished if elves were speaking that language (since in Iceland there /are/ elves, this might be a fact anyway :o) )
French is very beautiful too, not only because of its sound, but also because of its style of saying things, for example they say:
"coucher à la belle étoile" (sleep at the beauty of the stars)
for "to sleep under the open sky"
how beautiful is that, in German it is also (like in English) "unter freiem Himmel schlafen" that sounds like cold and military.
I can't think of an ugly sounding language though, imho all languages have their advantages and disatvantages, but in the end a language can't be ugly only the character who uses it.