What's the difference between these two?
Which is better/faster/reliable?
SCGI (like FastCGI) is a (serialized) protocol suitable for inter-process communication between a web-server and a web-application.
WSGI is a Python API, connecting two (or more) Python WSGI-compatible modules inside the same process (Python interpreter). One module represents the web-server (being either a Python in-process web-server implementation or a gateway to a web-server in another process via e.g. SCGI). The other module is or represents the web application. Additionally, zero or more modules between theses two modules, may serve as WSGI "middleware" modules, doing things like session/cookie management, content caching, authentication, etc. The WSGI API uses Python language features like iteration/generators and passing of callable objects between the cooperating WSGI-compatible modules.
What's the difference between scgi and wsgi?