btw- I read Pragprog's "Ruby Performance Optimization" (which is slightly out of date, but still awesome) and the short answer to which Ruby to use is the latest if you want the fastest performance. Since, say, 1.8/1.9 the major differences are big gains in speed. I haven't yet played with the new JIT stuff in 2.6, but it looks cool. I also read that they are thinking there should be a 3.0x speedup for Ruby 3.0 on top of that when it comes out. All those speed improvements compound to a much faster Ruby compared to older releases that are typically included on most OSs by default.