[seanmcdirmid]

I think if you are exploring the city during rush hour, sure subway makes sense. If you have a fixed route you go between everyday and know when the traffic ebs and flows, taxis are much more convenient. If you are out at night after rush hour, then taxis are the obvious choice.

Beijing's subway system is crowded, some routes are super crowded (line 10, ugh), interchanges can be long and windy, and can also have their own long lines (e.g. transferring at dongzhimen during rush hour). There are a lot more lines definitely then when I started living there (2007, line 10 didn't even exist yet), but there are very good reasons didi is still extremely popular.

[isostatic]

The system can be crowded, but not as crowded as Tokyo or even London IME (very limited experience of course)