choosing a wsgi server

Working on, we have a few different WSGI applications, and some WSGI middleware that we run across all of them. Some of the WSGI applications are Django, some are custom built, and we're planning to deploy some based on lazr.restful. Currently we run a mildly complicated proxy in front of the WSGI servers made out of a mix of Apache, squid, and haproxy - then we run several instances of each of the WSGI servers behind the proxy. We are using paste.http, but I want to switch to something with some more options. At the top of my list currently is spawning, but there are other interesting options like cogen and of course mod_wsgi. Although there are lots of interesting servers to choose from, it's hard to tell a clear winner or one that people are definitely having good success with in medium to large sites (sites with proxies, multiple app servers, multiple databases, etc.). I'm working on packaging spawning (and eventlet and greenlet) for Ubuntu now, but if there is another amazing WSGI app server out there I'd love to hear about it.