Your best choice for achieving your long-term goal of maintaining a single source codebase for iOS, Android, AND the Mobile Site is to stick with Angular + TypeScript + Ionic 2. This is because Ionic is fundamentally based on HTML, CSS, and JavaScript, the native language of the web. This crucial feature allows you to reuse the entire UI structure and logic of your application to deploy directly to a web browser as your Mobile Site (PWA/web app), maximizing your code efficiency. While NativeScript provides superior native performance by directly rendering native UI components, it uses XML for the UI. This XML UI code cannot be rendered on a standard web browser, which would immediately force you to rewrite a separate HTML UI for your Mobile Site, completely defeating your primary strategic goal of unified maintenance. For the vast majority of business applications, the slight performance difference is a worthy trade-off for the massive gain in development speed and maintenance simplicity that Ionic provides across all three platforms.