MoarVM is the closest to "ready", and seems to be what most of the developers actually using Perl 6 today are using. But, as the prior post mentioned, Rakudo-JVM and Rakuda-Parrot are also getting closer to ready. All of them will likely "ship", as long as the developers keep working on them, and Perl 6 code will likely run correctly on any of them.
Here is the current feature test statuses of the Perl 6 compilers/runtimes: http://perl6.org/compilers/features
Note that the Rakudo-MoarVM runtime is the closest to feature complete, with Rakudo-JVM close behind.
In short, you can expect you'll get whichever runtime you install, and if that runtime is ready for production you can expect that Perl 6 will work on that runtime. MoarVM will likely be the first to be ready for production.
You may have other reasons for choosing a runtime; if you have a Java/Clojure/Scala shop and wanted a powerful scripting language to integrate into your systems, the JVM runtime might be just the thing. If you wanted the fastest Perl 6 for standalone Perl 6 applications, MoarVM will likely be it (I think, I haven't looked at benchmarks, just guessing). The FFI may be easier to work with in MoarVM, if you need C or other compiled external libraries...but maybe not. I'm not at all familiar with how that works in JVM runtimes, but it seems like it would be more convoluted.
