React Native or Xamarin Forms for native app ?

Thanks for all the replies!
I think I'm going to go with React Native... Although I'm definetly going to check out expo.io !
Also learned about Turboliks existence which I want to check out as well!

I like React Native. I’ve been using it for my employer’s mobile apps for over a year and have barely had to write any platform-specific code. The documentation is really good too.

Check out expo.io

From my humble experience - don't mess around with MS as part of your solution's tech stack. Fragmentation of .NET and its libraries is just insane. Azure is a pain to maintain and badly documented. VS is buggy and slow. Choose Ionic or React Native for a long term play.

Isn't native app the opposite of React Native / Xamarin Forms?

Either way, I vote Flutter.io

Out of those two choices, 100% hands down React Native.

I'm a Xamarin developer so I'm clearly biased, but if you know C#, it's a good choice. Depending on the complexity of your UI, you could get away with using Xamarin.Forms, which allows you to share most of your core logic and your UI.

In the near future, I'm going to start on my own mobile app for my marketplace startup and I'll be using Xamarin.Forms without hesitation.

What stack is the web app developed in?

I've spent the last week making a hyrbid Android app for habitrabb.it using the Turbolinks Android wrapper. That has actually been a really quick solution.