I am talking about gradual typing here. Types are optional, if not given or implied they default to any. No need to annotate anything. If given they are enforced, and lead to optimized op codes and errors if violated. Some at compile-time, some at run-time. If fully typed, all errors are caught at compile-time already.

Duck typing as done with python is the worst of both worlds. No optimizations, no enforcement. Just optional external typechecks.

Of course untyped code (ie runtime types in each var) is to write faster. You only need to add types to some vars or args, and gradually improve from there. Eg ints only, because they are optimized the easiest. No need to check for strings, bigint, floats,.... Or arrays to check for overflows at compile-time and restrict to ints or strings. Massive improvements possible, in size and runtime.

Or object fields. Hash lookups vs static offsets.