When comparing Scala vs Pony, the Slant community recommends Scala for most people. In the question“What are the best (productivity-enhancing, well-designed, and concise, rather than just popular or time-tested) programming languages?” Scala is ranked 21st while Pony is ranked 22nd. 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 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
Pro Concurrency model based on actors
The unique type system allows the compiler to automatically schedule actors on threads, giving you reliable concurrency for free.
Pro Reliable
Because of its capabilities secure type system, provided you don't use the C FFI, references will never be stale, race conditions are effectively impossible, deadlocks don't happen because locks and mutexes are never needed, and processes never crash because all exceptions must be handled. (Barring compiler bugs or external memory corruption, of course.) Pony programs can still lock up due to infinite loops, like any Turing-complete language.
Pro High performance
Compiles to native code, and features an intelligent garbage collector that takes advantage of the actor architecture to get essentially free garbage collection.
Pro Trivially simple C FFI
Calling low-level C functions is as simple as use "lib:clibrary"
and @c_function_name[return_type](parameter:type)
. Linking C to Pony libraries is just as easy, as the Pony compiler will generate appropriate header files.
Cons

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.
Con All exceptions must be caught
The compiler enforces this, so code is littered with try
s.
Con Limited documentation
As Pony is such a new language, documentation is relatively light, and tutorials are few and far-between.
Con Few libraries
Con Garbage collector can't run until you yield
A long-running behavior can leak memory because the garbage collector has no chance to run.
Con Limited tooling
There's no IDE. Debuggers are fairly basic. Pony is too young to have much of an ecosystem.
Con Divide by zero is allowed
And instead of some sensible result like NaN or Inf, the answer is zero! Most languages would just raise an exception (and Pony used to do this), but since the compiler enforces the rule that "all exceptions must be caught" the proliferation of try
s was determined to be too burdensome on the programmer. This makes the whole design of the exception system questionable.
Con Unstable API
Pony is not ready for production. It has yet to release version 1.0, and there are frequent breaking changes.
Con Difficult learning curve
The type system uses a capabilities-oriented approach to reference semantics, which can be difficult to wrap your head around at first. The lack of more common object-oriented features and the preference for simplicity over familiarity can make it difficult for new users to model their program design.
