of course,is the first,第一个更符合语境

"在上海人很多" means that there are many people in Shanghai.(beaucoup de gens) "在上海人口过多"means that there are too many people in Shanghai.(trop de gens) If you want to stress the astonished population, you'better use "在上海人口过多".But the first one is also good.

Bonjour,Li qin. You want to know how to say" There are too many people in Shanghai". You can say:上海太多人了 or 在上海，人太多。Well,you can also say 在上海，人过多。 You know, in Chinese words 太多 is the same as 过多.You can use the one you prefer to. But ''很多'' is different from ''过多''.Let me show you some example as follow. 法国有很多美食。（There are lots of delicious food in France.） 很多中国人喜欢到巴黎购物。（A great many Chinese like shopping in Paris. ） 在上海人很多。（There are many people in Shanghai.） Finally,I will tell you how use ''在上海，人太多了'' in the daily converations. For example A:公车挤满了人！!（People crowd the bus.） B:是啊，在上海，人太多了。（That's right.There are too many people in Shanghai.） Well,that's all.希望能帮到你。

在上海人很多 In Shanghai there are lots of people. 在上海人口过多 Shanghai is overcrowded / Shanghai is overpopulated.

Thanks :)