Eggplant I say is good for cross platform tests or if you are testing something that's a thin client (for example something on a presentation server or virtualized desktop) as it's visual recognition vs. property specific.
Ruby + Selenium? Overall as a scripting language I like Ruby. The IRB interactive interpreter and polymorphic features of Ruby makes it easy to debug scripts in real time. I however prefer Java as compiled languages are generally faster and easier to develop framework code on (I work mostly in test framework design/implementation).