IntelliJ 12's Android support is vastly superior to Eclipse, in addition to being just a better Java IDE overall. I'm now very curious to know just how different Android Studio will be from IntelliJ.
I'd guess it's going to something akin to the difference between JetBrains' RubyMine and Ruby/Rails plugin support inside IntelliJ -- same overall functionality with better UX integration for the domain.
If you switch the preview released today[1], it's nearly the same as Intellij (even the build numbers almost line up at 130.xx). I just prefer the Intellij preview for some of the features one cannot get in the Android focused IDE Google previewed.
I'd guess it's going to something akin to the difference between JetBrains' RubyMine and Ruby/Rails plugin support inside IntelliJ -- same overall functionality with better UX integration for the domain.