Scala parser combinators vs ANTLR/Java generated parser?

I wouldn't worry about the performance limitations of parser combinators unless you were planning on parsing algebraic expressions that are a few pages long. The Programming Scala book does mention that a more efficient implementation of parser combinators is feasible. Maybe somebody will find the time and energy to write one.

I think with ANTLR you are talking about two extra build steps: ANTLR compiles to Java, and you need to compile both Scala and Java to bytecode, instead of just Scala.

Scala's parser combinators aren't very efficient. They weren't designed to be. They're good for doing small tasks with relatively small inputs.

So it really depends on your requirements. There shouldn't be any interop problems with ANTLR. Calling Scala from Java can get hairy, but calling Java from Scala almost always just works.