When comparing React Native vs ASP.NET Core, the Slant community recommends ASP.NET Core for most people. In the question“What are the best tools for making a cross-platform application?” ASP.NET Core is ranked 9th while React Native is ranked 10th. The most important reason people chose ASP.NET Core is:
Thanks to breakthroughs in ROSLYN compiler and the efforts of the .NET COre developer team, code written in C# can reach speeds just a step behind C++.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Allows you to develop native apps
React Native allows you to create native apps by generating native views with JavaScript instead of using a web wrapper.
Pro Large, supportive community
Despite being such a young framework (early 2015), the support for React Native grew quickly. There is a forum, active tag on Stackoverflow and many other ways to get help from the community.

Pro Backed by Facebook
Facebook writes their mobile apps in React Native so the code base gets pretty thoroughly used in some highly demanding scenarios.
Pro More predictable control of the state
The one way data flow, makes it more predictable and easy to control.
Pro Fast and getting faster
Thanks to breakthroughs in ROSLYN compiler and the efforts of the .NET COre developer team, code written in C# can reach speeds just a step behind C++.
Pro Multi platform
Can run on Windows, Linux and Mac (also Visual Studio Code editor).
Pro JSON optimization
In .NET Core 2.1 and 3.0, new APIs are added that make it possible to write JSON APIs that require less memory, using Span<T> and UTF8 strings, and improve throughput of applications like Kestrel, ASP.NET Core web server. See also Utf8JsonReader.
Pro Tutorials and documentation quality
Both microsoft and 3rd party tutorials are mostly of high quality and encourage you to use the industry best-practices.
Pro Built-in middleware
Built-in middleware featuring: Authentication, Cookie policy, Health Check, MVC, Session etc.
Pro Hosting
Ability to host on IIS, Nginx, Apache, Docker, or self-host in your own process.
Pro Ease of Use
Pro Security
It is a very secure platform.
Pro Tooling
Both VS and VSCode are powerful free IDEs that are well integrated with ASP.net Core. VS Community also allows for commercial use for projects with less than 5 developers.
Cons
Con If core team doesn't use a certain feature, it's not developed
Whenever there's functionality you need that they don't use in their apps, it's not going to get developed by them, even if it's obvious it should be in the core. They always say to either submit a PR or create a separate module.
Con Steep learning curve
React Native is not the most beginner-friendly framework for creating mobile apps with JavaScript. It requires that the developer know React, which is known to have a steep learning curve.
Con Many existing JS libraries are not usable on React Native; not exactly a 1-to-1 experience to writing React either
Example: Library that provides a full calendar with agenda view.
In the end it's much easier to develop in actual JavaScript with a solution such as Ionic, especially if your app needs to work well on the desktop.
Con React native only supports react which is getting old
React native is only based on react which is getting old. An old tech developer can't take much breaking changes so it gets more patchs. There is a limit, and react is too verbose and complex. better alternatives available today.
Con Microsoft environment
