Guangzhou. Has some old stuff to look at. Shenzhen is just a generic big city. The main good thing about Shenzhen is that it is easy to get to Hong Kong... 

The two are just a quick dash on CRH from each other, if you spend a week in one, going to the other for a day is not a big problem. 

Gz Vs Sz.....are we talking de guo you wrestling?

First pin to Sz but Gz has the staying power

The eternal question.

Guangzhou is more traditional, Shenzhen is more modern.

In Guangzhou the main language is Cantonese, in Shenzhen it's Mandarin.

Guangzhou is the center of Cantonese culture, Shenzhen is a melting pot of people from all over China.

Guangzhou has thousands of years of history, Shenzhen is a boom city with its history starting in 1979.

Now for Guangzhou if you like real China you will find it in the districts of Liwan and Yuexiu, the city's economy revolve around services, it has a unique taste as it's where the Cantonese culture was born.

Shenzhen has ultra-modern infrastructures and buildings, some of the craziest /most ambitious construction projects in the world are in Shenzhen, the economy revolve around high-tech and manufacturing, streets are cleaner, HK is just across the border.