When comparing React Native vs Appcelerator Titanium, the Slant community recommends React Native for most people. In the question“What are the best frameworks for developing cross-platform mobile apps with JavaScript?” React Native is ranked 2nd while Appcelerator Titanium is ranked 19th. The most important reason people chose React Native is:
Facebook writes their mobile apps in React Native so the code base gets pretty thoroughly used in some highly demanding scenarios.
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Pros

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 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 More predictable control of the state
The one way data flow, makes it more predictable and easy to control.
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 Provides a native experience
Through using Titanium's API and UI components similar to that of the platform's native UI, Titanium provides a native experience.
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 Commercial
Prices start at $39/month for an indie subscription. For a team account, the price is $249/month per seat.
Con Most plugins are paid
Appcelerator Marketplace is meant to sell to developers 3rd party plugins and functionalities as well as code samples. Thus, people will prefer to sell you their plugins and samples instead of making them open source. This will increase costs of development.
Con Lack of capabilities
For example, there is no way to read QR codes natively.
Source: https://stackoverflow.com/questions/40215208/qr-code-reader-on-appcelerator-titanium-alloy