v3.0 has a new API that is not backwards compatible. However, the v2.1 API is still supported, but it is tagged as deprecated.
You should know that v3.0-pre-alpha0 does NOT have the final API and more changes will be added in the next releases.
If you plan to release your game in the next 3 months, I suggest to use v2.1.4.
But If you plan to:
- release your game next year
- and you don’t mind upgrading your code during these months in order to use the new APIs
- I suggest start using v3.0-pre-alpha0.