Hot on the heels of his Windows Ruby implementation shootout comes Antonio Cangiano's Great Ruby Shootout of July 2010 where Antonio pits 8 different Ruby implementations against each other in a performance shootout!
Antonio's findings and observations are interesting and well worth a read (particularly the parts about memory consumption) but if you're in a hurry, the conclusion is that Ruby 1.9.2 RC2 and JRuby 1.5.1 are almost joint first place for fastest Ruby implementation (but 1.9.2 takes it by a hair.) Ruby 1.9.1 and Maglev are then very close behind.