Taiwan! ;)

I agree Beijing is the best choice. I was born here, and I'd be happy answer your question about trip in Beijing.

The second city is Xi an. I've been there 3 times. It is very amazing.

Xi an is the capital of Shaanxi province, and a sub-provincial city in the People's Republic of China. One of the oldest cities in China, with more than 3,100 years of history, the city was known as Chang'an before the Ming Dynasty.[1] Xi'an is one of the Four Great Ancient Capitals of China, having held the position under several of the most important dynasties in Chinese history,including Zhou, Qin, Han, Sui, and Tang.Xi'an is the eastern terminus of the Silk Road and home to the Terracotta Army of Emperor Qin Shi Huang.http://en.wikipedia.org/wiki/Xi'an

come to my beijing!

I agree with Allen. Big cities are probably better for you because some western people said they are uncomfortable with those attentions when they are walking on the streets which will happen if you go to a small city. Big cities include Beijing, Shanghai, Shenyang, Nanjing and other capital cities. Good luck to your 'adventure'!

In my opinion , the big city would be preferable for most foreign tourists first time to visit Mainland China . You can be familiar with their culture and living manner in metropolis sooner than some other rural areas. I heard a foreign tourist was warned to encounter criminal problem alone by train . I think that is not relatively safe to a alien tourist , so rather,  Beijing would be a good option for you as Kara advised above unless you have better idea.