I am a Rubyist that is just starting to dabble in Smalltalk and am trying to chose an implementation to experiment with. It seems like Squeak or Pharo would be a good choice, but I'm having trouble finding current information to help decide which one would be better. Much of what I find via Google searches is from a couple of years ago and may no longer be relevant.
Is there a clear favorite these days? If not, what are the pros and cons of each?
To certain extent, it is a matter of personal taste. Pharo is fork of Squeak intended make it more modern version of Smalltalk, sometimes at expense of not sticking to backward compatibility to Squeak.
Pharo being a fork, also means that they share much in common, from VM to huge parts of class library. Many add on packages work with both of them, and some are developed with Squeak as primary dev platform and I guess a slightly larger number of them are developed in Pharo (Seaside, Pier, etc). Both variants have free intro books: Squeak by Example, and Pharo by Example, but Pharo one seems more up to date.
Personally I prefer Pharo since it gives me cleaner and more modern feeling.