If you're thinking between Passenger and Unicorn, the main determining factor between the two is that Unicorn is most efficient when you're serving a single app

If you're thinking between Passenger and Unicorn, the main determining factor between the two is that Unicorn is most efficient when you're serving a single application in production. Meanwhile Passenger is best if you have multiple apps running on the same server. In terms of functionality (i.e., subdomain redirects) both are practically identical. The one functionality that's tougher is the ability to do streaming. In that case, you'll have to look at Puma, Rainbows!, or Thin. And in terms of deployment, you'll use Capistrano. You can use Jenkins too if you're looking to setup continuous integration, but you'll need Capistrano regardless in order to deploy to production.