It depends where he/she said " China is the best". In China, I would say: yes, it is In US, I would say: why don't you go back to China?

I would say "I do not know" since I know too litlle about China

No problem with that! It's about pride in where you come from. ^^ It's only if they say "China is better than (specific country)", then they have an interesting discussion to follow. :) Uh - Martini? I think you mean Canada? I can't imagine candida being the best. O_o

"jiayou, China"

I would say...Ni zhi dao--ni hen chong ming? wo hen xihuan zhongguo...but I'm not chinese...but I can speak it.