Vue 3 is the current, latest major version of Vue. It contains new features that are not present in Vue 2 (most notably Composition API), and also contains breaking changes that makes it incompatible with Vue 2. Despite the differences, the majority of Vue APIs are shared between the two major versions, so most of your Vue 2 knowledge will continue to work in Vue 3.
In general, Vue 3 provides smaller bundle sizes, better performance, better scalability, and better TypeScript / IDE support. If you are starting a new project today, Vue 3 is the recommended choice. There are only a few reasons for you to consider Vue 2 as of now:
You are still waiting for major ecosystem projects like Nuxt or Vuetify to release stable versions for Vue 3. This is reasonable if you do not wish to use beta-stage software. However, do note there are other already stable Vue 3 component libraries such as Quasar, Naive UI
and Element Plus
Vue 2 has shipped a final minor release (2.7) in July 2022, which backports a selected subset of new features from Vue 3. Vue 2 has now entered maintenance mode: it will no longer ship new features, but will continue to receive critical bug fixes and security updates until the end of 2023.