I know I'm cheating by recommending both, but that's because I don't think you can go wrong either way.
At the end of the day, I would go with the language that you enjoy writing the most as you'll be using it a lot in your workplace. If you aren't having fun at work, that's a lot of time spent suffering.
Ruby on Rails is far from being dead. In fact, this is a very popular choice in early-stage startups, given how fast and easily it allows them to launch their product and iterate on it.
Even at more mature companies, you'll still find a ton of opportunities. Not for internal tools or legacy codebases, but for actual production workloads: web apps, APIs, etc...
Some may tell you that Ruby doesn't scale, but is it really Ruby that doesn't scale, or the code they wrote?
Languages have trends. Sometimes, recruiters will try to take you one way or another to meet their own agenda. Don't always listen to what you hear. Long live Ruby! Long live Rails!