Jared Friedman recently wrote a really great article on why he wouldn’t use Rails for any new company. There are a couple of factors that he looks at that makes this a really well written article.
First, he uses data to show the rapid decline in Rails usage by looking at Google Trends. Then he looks at Rails biggest performance headache: ruby. He compares benchmarks of Ruby to other languages. He points out that Ruby has no major corporate sponsor. He also points out the newer growing frameworks around and the job trends on Indeed.
This is a really good article, I would encourage you to check it out and read the Hacker News comments too.