Ruby instead of Perl5 (not Perl6)? Because I found Perl5 really hard to write maintainable comprehensible code in, requiring weird magic boilerplate, and full of gotchas. Could just be me, maybe could have been overcome, was just my subjective opinion. And I like writing OO code in Ruby style. Also, like many others, what brought me to ruby was wanting to check out Rails (although now I'd say I have fonder feelings for ruby the language than I do for Rails the framework). All just my own opinions and experiences.
Those sorts of answers from other's perspectives is what i'm interested in for Perl6 (not 5) over ruby. I think I know many reasons to prefer perl5 over ruby (although I don't), but once you leave perl5 for perl6... I'm not sure why you wouldn't just ruby (or python). But could be just cause you're used to Perl and like Perl. Or could be because there's something about Perl6 you especially like over ruby/python. Etc. I think it's a reasonable question?
You wont get many opinions of people's experience of Perl6 from Hacker News. Just a lot of rage and assumptions it's somehow just like Perl5, which it's not. There are only a few of us (tens, maybe a hundred very quiet people) actually writing it daily. With no official "released" 6.0.0 version it's not supported that well by Linux distros yet either. Like if you install Rakudo on Debian stable right now it would be about two years out of date iirc. In the last two years a custom Perl6 VM was written with a JIT compiler and tonnes of concurrency stuff was added! You can however easily install it yourself and keep up to date with rakudobrew http://perl6advent.wordpress.com/2014/12/02/day-2-rakudobrew...
My $0.02 is you'd mostly want to learn Perl6 if you were after something like Ruby but perhaps with more room to express yourself and form a community and build new technologies. At least I really love the language and find it very expressive and intuitive to use and it has a lot of features useful for doing Bioinformatics built in (something I'm going to add to the P6 advent calendar on the 15th Dec). The extra level of detail ten years of design puts into a language like all the funky features working together and being consistent helps a lot. So much of the cooler expressive/functional stuff in Python feels out of place like lambda and list comprehensions. Maybe I'm wrong but I wouldn't write anything /that/ complicated or important using Python lambda or list comprehensions. They just don't play that well with the surrounding code you will have to write in a different style. I can't attest to Ruby since I don't know it well. I felt it was quite close to Perl and I'd be better placed learning Python instead, especially for a job writing code that wasn't for the web.
Perl 6 tries to address many of the Perl 5's gotchas, including OO. Throw in familiarity into that and a lot of new features that scratch various itches and you would understand why some Perl 5 people would want to try Perl 6, but not Ruby.
Maintainability, productivity, etc. of Perl 5 is on the same level with Ruby. And I don't think Perl 6 improves on that, so it's probably the same too.
Personally I don't see any benefit for anyone to switch between mentioned languages. They all have similar problems.
Those sorts of answers from other's perspectives is what i'm interested in for Perl6 (not 5) over ruby. I think I know many reasons to prefer perl5 over ruby (although I don't), but once you leave perl5 for perl6... I'm not sure why you wouldn't just ruby (or python). But could be just cause you're used to Perl and like Perl. Or could be because there's something about Perl6 you especially like over ruby/python. Etc. I think it's a reasonable question?