Guangzhou in general, Panyu in specific.  Shenzhen is too expensive and tries too hard to be Hong Kong and fails miserably at it.

I agree with John, Guangzhou is definitely the city I favor more.  Shenzhen is very expensive, and doesn't have much, if any of the charm that is great about Chinese cities.  It is nice to visit as a day trip, but I don't think I could fully enjoy living there.  Guanzghou is filled with tons of great small shops and places to eat around every corner.  Being an important trade city, everything can be bought cheaper, except the coffee of course.  Shenzhen doesn't have any of this due to it being a new city, it is designed to mimic large western style cities and Hong Kong.  If you live in the right areas, GZ is convenient and cheap to travel around the city.  Shenzhen, Dongguan, Macau, Zhuhai, and HK are only a 30 to 45 minute train ride away for pleasure and visa runs.

While John above prefers Panyu, I'm happy up in the center by the Dongshan area of Yuexiu.  I don't think you can go wrong with Yuexiu if you can find a modern house,  Panyu (though more travel time to the center), Haizhu district near Jiangnanxi (younger crowd here) and parts of the Tianhe district (if you can afford it) are all great choices.

I lived in TianHe in my Guangzhou days.  I found the area rather antiseptic and devoid of any form of interesting life.  Very Riverdale, New York so to speak.  In the end, I moved to Xiamian Dao which is the great little historic island in the old part of the city.  It used to be the foreign concession part of the city and nearly 90% of the old historic buildings are still there.  It was such a 19th century European feeling.

I live in Shenzhen :(

Never been to Guangzhou.

without any doubt it is Guangzhou..981..question is also from you and there is answer also from you..

I have no experience to judge how Guangzhou compares with Shenzhen. However in the many times I have spent a day or perhaps several days in Shenzhen, I would say the city has much to be favored. Above comments about modernity being a big factor. Shenzhen often does feel quite modern to me, but that goes without saying considering their history.

Guangzhou on the other hand... well, for large cities in China, this is my favorite. Next being Nanjing, and then Shanghai. And small cities, it would have to be Zhanjiang, Guangdong. 

Anyways, back to Guangzhou, I really don't know why I love GZ. I just do hehe... there is always something interesting about this city. You just have to go out and find it. 

don't wanna live in either...even Xiamen is too big for me...would move to Zhuhai or something if I had a chance

Cleveland- hands down.

I like Guang zhou as well, becasuse it is near my home, more easy for me go back home...

How I wish I could work in Guang zhou city, it's a pity currently I am working in Dong guan city....

I prefer GZ over SZ for the simple reason that GZ has more than 2,500 years of history whereas SZ was nothing more than a fishing village less than 30 years ago.  Lots of interesting spots in GZ but in SZ everything they've built recently are all attempts to be like HK.  

SZ is too spread out and difficult to get around. If you have friends in Shekou and want to go to Louhu you are looking at an hour plus on the metro either way. Too expensive. But I do think the nightlife in Shenzhen is a little better. A few more tourist attractions.  

Love the same girl in GZ and SZ..then you will conclude yourself..

For me, the most precious things under the heaven are green streets and mountains, a lot of parks, flowers, trees, fresh (sea-) air and rich reigns, blue sky (no smog) and sun, calmness (no industrial and urban noise). That is why SZ is much preferable than GZ or HK. ( I remember during my visit to GZ in my Hotel room I could find a respirator on the table for protection of breath... I had been shocked: how people can survive here?).

GZ also has some points I greatly like - its historical places - anciant temples (Liurong, Wuxian guan, Guanxiao), an outstanding Museum (Nanyue Kings tomb), Wongpu Military Academy, Agricultural movement Institute.

So, when I come to Guandong I use to stay at SZ, but sometimes visit GZ or HK to see their historical places.

By  the way, city library in SZ is much better and richer then in GZ, HK`s library is rather comfortable, but books are very poor, much poorer even than GZ`s.    

Guangzhou is better for life, Shenzhen is better for fighting!