Quote
Cris
1. Cantonese is a much older and much purer Chinese language than Mandarin
In some ways yes, and in other ways no. Both share an ancestor in Middle Chinese (中古漢語), from which Cantonese has preserved its tones and codas, and from which Mandarin has preserved its medials and retroflex initials. Both languages, unlike Shanghainese (for example), suffer from the loss of voiced initials. While the abandonment of the entering tone, the initial /ŋ/, and the coda /m/ in standard Mandarin is annoying, the abandonment of medials (aside from the two instances of /w/) and retroflex initials in standard Cantonese is equally annoying.
Quote
Cris
2. Cantonese was the native dialect spoken by Sun Yat Sen father of modern China
That's nice. What do you think 孔子 and 康熙帝 spoke? Hell, 吳敬恆 was one of 孫中山's best buddies, and he was the principal architect of 國語注音符號 and the standardisation of Mandarin, something that the good doctor approved of.
Quote
Cris
3. Cantonese have 6-9 tones while Mandarin has only 4 tones
Middle Chinese (中古漢語), a far purer Chinese language, had four tones (three of which overlap with Mandarin). Is it the number of tones with which you're concerned, or the nature of the tones themselves?
Quote
Cris
4. Cantonese rhymes with ancient Chinese poems especially with Tang poems
That's nice. If I wanted an authentic recitation of 唐朝 poetry, I'd prefer to hear it in the language of the time anyway.
Quote
Cris
5. Cantonese retains many ancient words/vocabulary of ancient Chinese language
As does standard Mandarin. There are plenty of examples where Cantonese uses older vocabulary than Mandarin (e.g. 食 vs 吃, 飲 vs 喝), examples where Mandarin uses older vocabulary than Cantonese (e.g. 不 vs 唔, 在 vs 喺), and examples where they both adopt modern colloquial forms (e.g. 的/嘅 vs 之, 甚麼(啥)/乜嘢(咩) vs 何).
Quote
Cris
6. Cantonese can express themselves better than Mandarin
What does expressing themselves better mean? Do they have a more expansive and nuanced lexicon from which to draw? Is it because they can say the same thing in fewer syllables? You can convey ideas in Classical Chinese (文言文) even more succinctly, and yet it is nonetheless ill-equipped to discuss many modern topics.
Quote
Cris
7. Cantonese when written is more difficult but perfect for communication and instant chatroom
Cantonese is arguably easier to understand verbally than Mandarin because of fewer homophones, but Cantonese has also increased in homophones (to a lesser extent) over the last century due to the merger of alveolar and post-alveolar/alveolo-palatal initials (e.g. 沙 'shaa1' becomes 'saa1'). For those who use lazy speech, the homophone count is further increased.
Quote
Cris
8. Cantonese is the language of democracy/freedom where as Mandarin is the language of Communism in China
This assertion is completely ad hominem and irrelevant to language, not to mention the fact that Mandarin is the official language of the Republic of China. Do you think that simplified characters are communist too?
Quote
Cris
9. Cantonese is the only language among Chinese that is close to ancient Chinese and have official status
All of the Min (閩) varieties are actually a lot closer to ancient Chinese than is Cantonese, as this language branch split from the main Chinese lineage prior to the rise of Middle Chinese (中古漢語). If I recall correctly, Minnan Hokkien (閩南福建) has some kind of official status in the Republic of China, but someone please correct me if I'm mistaken.
Oh yeah, this is all assuming that we agree on "older is better", which isn't necessarily the case, as others have correctly noted.
---
I clearly support Cantonese to some extent, since I'm a member of this forum, but to borrow the phrasing of the late and great Steve Jobs: "Mandarin doesn't have to lose for Cantonese to win".