Ranked in these QuestionsQuestion Ranking
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.
Pro Great developer tools debug/hotreload/analyser
Pro Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers.
Pro Open source
Pro A single codebase for iOS AND Android
The developer's goal is to allow people to make apps running at 120 FPS.
Con Has specific requirements with regards to installed libraries
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.
Con Still in development
According to the website, Flutter is still in its early stages of development.
Con Dart is unpopular and never gained serious community traction like Kotlin or Java
Con Does not support 32-bit iOS devices
If you plan on targeting iPhone 5, 5C or earlier, you can forget about Flutter.