I would choose Rails if my biggest concern were time to market and server costs weren't a huge concern. For any kind of site where you're selling a service or product and for the vast majority of freemium models, Rails is great. You'll have to scale a bit sooner than if you chose something like PHP, Node or Go, but you'll have plenty of revenue to pay for it. You'll also either get to profitability or to the point wh…
Why compare rails to PHP and node for server costs? They are all similar. If you care about server costs you use Java or Scala or something with actual performance...
1) PHP and Node both tend to get significantly better performance than Rails. Either is more than sufficient for free products. See: Facebook, WordPress.com, Medium, etc...
2) Java does well in numerical processing, but it isn't necessarily more performant than node or PHP as a web server and it's a bit of a memory hog. Keep in mind Paypal realized huge gains from rewriting large parts of its Java back-end into Node a few years back. Ditto for Groupon.
3) If you're really worried about web server performance, you're probably better off going with Erlang/Elixirm, a JVM language or Go. If you have something truly massive (e.g. Google/FB/Amazon), then you'll probably hire teams to write infrastructure code in C++. Doing that for a normal web app would be nuts.