I use and love JRuby on daily basis, but I suggest you use MRI (a.k.a. C-Ruby) unless you have a actual need for JRuby.
Reasons for using JRuby:
- Java integration
- Restricted environment (your machine has Java installed by not ruby and you don't have root)
- Restricted environment (you have ruby installed but don't have root so can't install gems you need)
- You reached the limits of Ruby 1.8 performance and cannot use 1.9
From what you've described, you don't have any of the above reasons.
C-Ruby 1.9 has significant performance improvements over C-Ruby 1.8. I've yet to read (or find out for myself) how C-Ruby 1.9 compares with JRuby 1.8 or JRuby 1.9. In anycase, you don't have a performance problem (yet) so don't worry about it.
The good news is, you can start with either and convert later if needs be. It's all Ruby, and the Webrick and Mongrel gems work with both.
As mentioned above, ruby gems that have C extensions cannot be installed under JRuby. Hopefully this will change in the future if ruby C extensions utilize FFI.
