I've been building for the web for 15 years, and Aurelia feels more natural to me. Granted, my Angular projects were all in Angular 1 and it has since undergone a massive rewrite, almost as if it's a different framework now. But based on my extensive experience with web applications using Java, Ruby and Node.js on the servers (sometimes Single Page Application frontends, sometimes minimals JS with jQuery libraries, etc), Aurelia just felt more naturally web-like. That doesn't mean Angular is not able to do the job, but it feels more like using a heavier tool that doesn't belong.
Aurelia also feels easier to build with (less unnecessary boilerplate) and more maintainable in the end. The community is small but has made immense strides in a short amount of time. There is a company backing it, but a very small one, not a giant one such as Google or Facebook (and those giant ones make no guarantees, but the small one backing Aurelia has emphasized their long-term commitment time and time again). They have an ever-increasing number of community contributors and features have been added at a rapid pace. Since I began a year and a half ago, UI toolkits have regularly added Aurelia integrations. The CLI has improved by leaps and bounds.
You can find out more on their website and other blogs and articles around the web, but you may find this helpful:
http://aurelia.io