I'm struggling to understand all the options as well. In this blog post I found some benefits of mod_wsgi compared to mod_python explained.
Multiple low-traffic sites on a small VPS make RAM consumption the primary concern, and mod_python seems like a bad option there. Using lighttpd and FastCGI, I've managed to get the minimum memory usage of a simple Django site down to 58MiB virtual and 6.5MiB resident (after restarting and serving a single non-RAM-heavy request).
I've noticed that upgrading from Python 2.4 to 2.5 on Debian Etch increased the minimum memory footprint of the Python processes by a few percent. On the other hand, 2.5's better memory management might have a bigger opposite effect on long-running processes.
