Varnish + Nginx for WordPress is Good?

Yes, it is good, but other options are also good.

There is no silver bullet in term of webservers and caching software, if there was everybody would have been using the same tools. It depends both on what are your actual needs and how comfortable are you with managing the tools.
For example it might be that nginx is somewhat faster then apache, but if you have already good knowledge of apache the cost of the time needed to learn nginx might be higher then the cost of upgrading the server.

WordPress is not tied too strongly to any webserver technology, therefor you should be able to experiment with different webserver configurations to find the one that works best for you without a need to make any changes in your code. That said, many tutorials on the web will assume that you are running on apache, and might give apache specific information, something that makes managing wordpress under nginx a little more challenging.