Some of the folks now work for JetBrains, thus InteliJ is the one with best support.
Then they decided to focus the remaining effort on Scala Metals, which is based on LSP protocol.
In both cases it is alright for Scala 2, there are some rough edges for Scala 3.
The compiler is faster than it was, but not exactly fast. SBT I avoid as much as possible, so can't really speak to that. The eclipse plugin is sadly abandoned, but IntelliJ has pretty good support.
I played with it a long time ago and the IDE (eclipse plugin?) was a bit of a mess, sbt was prone to weird issues and lock ups and the compiler was pretty slow.
Very fun language tho!