Talking purely economical the answer is simple, China is way better.
单从经济层面讲，我的回答很简单，中国要好太多了。
China is cheaper, and China`s economy is growing faster.
中国的生活成本更低，而且中国的经济正发展得越来越快。
Japan has 200% debt to GDP. For the rich or the poor, China is better economically.
日本的债务是GDP的200%。不管是对富人还是穷人来说，中国在经济层面都更好。
This is a nuanced question that deserves a nuanced answer.
这是一个微妙的问题，所以得用微妙的方式来回答。
If I were unskilled, low skilled, or in a conventional career, Japan is obviously the better place (assuming also I was Japanese!).
如果我是个什么都不会、或者技能有限的人，亦或是从事着一份传统职业，那日本显然是更好的选择。（如果我本人是个日本人，那就更是如此了！）
If I was a programmer/tech worked, entrepreneur, or high rolling exec/manager type who wanted to take lots of risks, well, china is obviously the better choice.
而如果我是个编程人员、技术型人员、创业者，或者是个慢不下来、喜欢冒险的C某O、管理人员的话，那么，中国显然是个更好的选择。
I guess the question assumes that you have the same income in each, not one in proportion to the average for that country?
我猜，这个问题的预设前提是：你在两边的收入是相等的，而不是根据那个国家的平均水平来变？

In that case, you can live a better life in China because the cost of living is cheaper.
如果是这样的话，你在中国的日子会更舒服，因为那里的生活成本更低。
This is talking economically, of course, not taking other factors into account.
当然，这只是从经济层面来讲，并没有把其他的因素纳入考虑范围。
Outside of first tier cities, the cost of living is far cheaper in China.
在中国，如果是在一线城市以外的地方，那生活成本会低很多。
You can live quite comfortably on a modest salary.
即使你的薪水只是中档水平，也能过得相当舒服。
If you're lucky enough to collect your western salary, life can be somewhat luxurious.
而如果你很幸运地拿着发达国家水平的薪水的话，你的生活甚至能过得很奢侈。
Finding a nice Chinese girlfriend or wife is just icing on the cake.
如果能找到一个中国女朋友或者中国太太，那就更完美了。
Consider the air pollution level first!
你先考虑考虑空气污染的问题吧！
The PM2.5 index, for examples.
比如去看看PM2.5的指数。