At the risk of offending people, the reality is that a language being older doesn't make it better, or cuneiform Sumerian would be the best language and oracle bone script would be the best writing system.
Also at the risk of offending people, a language typically is considered to sound smooth and melodic if it has low number of consonant endings outside N (in particular ejective consonant endings like -k, -g, -p, -t, -d), consistent sounding vowels, and vowel rich sentences.
That is why many people think Germanic languages (German itself in particular) are harsh sounding languages while Japanese and Latin languages like Spanish are considered to sound smooth - they tend to have vowel endings and non ejective consonant endings like -N or -S.
By that standard, standard Chinese is one of the smoothest sounding languages in the world next to Japanese, Spanish and Polynesian, with 0 ejective consonant endings, only vowel, N, NG and R endings.
Cantonese is on the other hand is like German, with multiple ejective -k, -p and -t consonant endings.
