Should I learn Laravel or Ruby on Rails?

I can't tell you what to choose, but I'll tell you my preference.
I used to code in PHP up until 2013. I launched a startup back then, and decided to dive into ruby on rails for learning a new language. I haven't looked back ever since.
Any project I started or worked for customers, it was always RoR. I haven't hit performance issues, scalability issues, and the development is pretty fast compared to PHP.
Bottom line - I would recommend ruby on rails, but it's really up to you and your preferences.

I think Laravel is inspired by Rails, so the concepts should be pretty similar. Both will enable you to do great applications and both will be here for a long time, so you can't really make a bad decision here. Take a look at both programming languages (PHP and Ruby) and decide whose aesthetics and expressiveness you like more.

If you already know PHP, go with Laravel. PHP and Laravel will be there for a long time. If you are looking to learn something from scratch, I would suggest JavaScript and/or Python though. You can make web apps using Express, Flask, Django.

Build a super simple app in both.
See how long it takes in each, which one you liked, had the best docs and tutorials for that you could actually follow.
You will only know by using them.
Dont worry about the longevity of them.. both have been around for ages and will be for a long time yet.

I think it's a wash. They're good at the same things and have similar (wonderful) communities. Rails is a bit more unified and Ruby is a bit more productive than PHP, but Laravel has a bit better performance / momentum in the community.

Either one is a fantastic choice for indiehacking. In fact after learning one well you can easily (and probably should) pick up the other and mess around to see a slightly different way of doing things.

If you already know PHP to an extent stick with that. There's not really anything that Ruby could do that PHP can't, so you'll be in a good place with PHP knowledge. It's good enough to get software out the door, and there is also a decent market for jobs (at least where I live) so you have a good range of options in the future. While PHP has lost a bit of market share, there's still a large thriving community around it.

If you really want to expand and start building applications I'd start looking at Javascript + React. Building your UI with Javascript/React and running the API with Laravel is a solid option.