Flutter and Ionic are both cross-platform frameworks for developing mobile apps. Ionic uses web technologies like HTML and CSS to create hybrid apps, while Flutter uses its own widgets and renders directly to native platform controls. Ionic apps may have poorer performance than native apps due to using a webview, while Flutter provides native-like performance. Both frameworks make developing for multiple platforms easier, but Flutter could have an advantage in terms of performance and integration with native features, while Ionic may be easier to learn for web developers. Developers must consider their needs and choose the framework best suited to their specific project goals and requirements.