In production, Apache + mod_wsgi or Nginx + mod_wsgi?
The main difference is that nginx is built to handle large numbers of connections in a much smaller memory space.  This makes it very well suited for apps that are doing comet like connections that can have many idle open connections.  This also gives it quite a smaller memory foot print.
From a raw performance perspective, nginx is faster, but not so much faster that I would include that as a determining factor.
Apache has the advantage in the area of modules available, and the fact that it is pretty much standard.  Any web host you go with will have it installed, and most techs are going to be very familiar with it.
Also, if you use mod_wsgi, it is your wsgi server so you don't even need cherrypy.
Other than that, the best advice I can give is try setting up your app under both and do some benchmarking, since no matter what any one tells you, your mileage may vary.
What to use for a medium to large python WSGI application, Apache + mod_wsgi or Nginx + mod_wsgi?
Which combination will need more memory and CPU time?
Which one is faster?
Which is known for being more stable than the other?
I am also thinking to use CherryPy's WSGI server but I hear it's not very suitable for a very high-load application, what do you know about this?

Note: I didn't use any Python Web Framework, I just wrote the whole thing from scratch.
Note': Other suggestions are also welcome.