When comparing Apache Groovy vs Scala, the Slant community recommends Scala for most people. In the question“What is the best programming language to learn first?” Scala is ranked 27th while Apache Groovy is ranked 63rd. The most important reason people chose Scala is:
The immutable values make it perfect for working with concurrency
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Integrates well with Java
This link adds some interesting points explaining how Groovy integrates better with Java than e.g. Scala. If you want to write classes that can be consumed by Java classes, or easily consume existing Java code, Groovy is probably a pretty wise choice. It can be statically compiled and supports optional typing, which makes it much more maintainable for larger projects than e.g. JRuby.
Pro Dynamic and static type checking and compiling
Pro Relatively large ecosystem
Groovy is a popular JVM language with a rather large and developed ecosystem. It has several web frameworks (the most famous being Grails) and many libraries.
Pro Closure support
Pro Nice syntax
Pro Immutable values
The immutable values make it perfect for working with concurrency
Pro Multiparadigm
Scala supports both Functional and Object Oriented styles of programming. Beginners can learn both paradigms without having to learn a new language, and experts can switch between the two according to what best suits their needs at the time.
Pro Type inference
Scala offers type inference, which, while giving the same safety as Java's type system, allows programmers to focus on the code itself, rather than on updating type annotations.
Pro Compiles to JVM bytecode
Aside from Java itself, Scala is by far the most popular of the many JVM languages. If you're developing for Android, or a similar JVM-only platform, or otherwise need out-of-the-box cross-platform compatibility, but the performance of a compiled language, Scala is the way to go.
Pro Very good online courses
On coursera you can find great introduction to Scala by Martin Odersky.
Pro Type inference leads to a simpler syntax
Pro Expressive functional programming abstraction for reusable and safe code
Cons
Con Compile Static and generics have some problems
Con Can be intimidating for beginners
Scala is an industrial language. It brings functional programming to the JVM, but not with a "start small and grow the language" perspective, but rather a very powerful language for professional programmers.
Con Way too complex for beginners
Even for seasoned programmers it's a difficult language.
Con Static type system inherits cruft from Java
The type system is too complicated yet still less powerful than Haskell's.