[tomfakes]

In my experience with both Passenger/nginx and Unicorn/nginx, Unicorn is much more under control with the number of processes it spawns. Passenger may have fixed this by now, but when I was testing, Passenger would forget about processes and spin up new ones. Eventually, you'd run out of memory and Bad Things would ensue.

Unicorn has never done that to me. For production use, that makes the decision really easy