Everyone agrees that hyphenated urls are better for SEO; Google themselves say you should prefer hyphens to underscores.
Hyphens are easier to type than underscores for the average user, less likely to be missed when reading, and again better for SEO in URLs
Rails generated routes should at least have the option to use hyphens in path output without needing to do resources "something-with-multiple-words", as: :something_with_multiple_words
To not break backwards compatibility, I was thinking a config flag for the application.rb
file like:
Rails.application.config.use_dashed_routes = true
With this flag, resources :something_with_multiple_words
would still point to the same controller and create the same path/url helpers, but the outputted path and route would generate and respond to /something-with-multiple-words
instead of /something_with_multiple_words