Java has been doing great recently and I feel there is a bit of a renaissance going on. There is a very mature leadership at the helm and it shows.
With .NET, it seems that they've added features too quickly without giving it enough thought up front. If you are a small team or working on a short lived project, this might not matter. But for long lived projects by large teams, I'd rather take the more conservative approach.
Java has been playing catch-up for a while after the ecosystem stagnated on Java 8. The language seems to be very willing to incorporate new changes, but most interesting improvements seem to be stuck behind "nth preview" developments (basically useless), or the release was as badly thought through as any C# feature.
For instance, Loom took ages to make it into Java itself, finally reaching an LTS version in Java 21, but it took until Java 24 for Loom to be able to deal well with any code hsi g synchronized {} blocks. They also went back on their previous advice ("change synchronized blocks to reentrant locks to fix compatibility") which must be fun news for the projects that did follow their earlier advice.
And while introducing modules and breaking the compile for any old Java project seems to have gone through without much trouble (throwing compiler warnings everyone ignores for several releases before breaking code, of course), the language seems to dread minor backwards incompatibilities when it comes to language level improvements like nullable types, introducing a tri-state nullability definition while also refusing to implement some stricter null checking to ensure the language feature is entirely opt-in.
Java feels like the backend is picking up features as fast as Javascript or Rust or C#, but the frontend is managed like C. A weird mix between "change is scary" and "stagnation is decline". It's the language at the forefront of high-performance dynamic programming while also having had an unimplemented "const" keyword for 25 years.
