<p>What's the difference between these two?
Which is better/faster/reliable?</p>

They are both specifications for plugging a web application into a web server. One glaring difference is that WSGI comes from the Python world, and I believe there are no non-python implementations.
Specifications are generally not comparable based on better/faster/reliable.
Only their implementations are comparable, and I am sure you will find good implementations of both specifications.
Perhaps
read
and
read
.