Chinese sure sounds ugly for an outsider and as Chinese are - for the moment - only good at copying and obeying like slaves, I also assume it's a slave language.
They even let men scream like little girls in their operas:
http://www.youtube.com/watch?v=zHPegoquV5I
I don't know which Sino-Tibetan language is uglier than the other, but Mandarin like in the clip sounds okay. What is an ugly Chinese language however is the following (which is also frowned at by Chinese themselves obviously lol):
http://www.youtube.com/watch?v=Qv9wk5lgGFo
Arabic can also be an ugly language, at least when spoken by religious nutters who even avoid neologisms. But Arabic is very diverse so there's also 'nice-sounding' Arabic.
Further are ugly languages:
Esperanto
Dunglish/Denglish and variants
As for the most beautiful languages:
German
Dutch
but not when they're spoken by someone who doesn't respect the language
Further are beautiful languages:
Turkish
Finish
Hungarian
also French sounds nice, sometimes
Berber languages also are cool
so are Celtic languages.
Not to be PC-minded, but personally I know little of languages being ugly. I can find the way they're spoken to be very ugly, but that's usually it. Usually languages can improve or decline, in my opinion.
Still, I can find some languages particularly awesome.