Here is my comparision of both environments:
Advantages of using Eclipse:
- popularity and great support
- many plugins
- free UML plugin
- better compiler (however you can use it from Intellij as well)
Disadvantages:
- slow (as you install more plugins)
- sometimes becomes unpredictable
Advantages of using IntelliJ IDEA:
- light-weighted and fast
- more intuitive interface
- intelligent code editor
- Android UI Designer (since ver. 12)
- free Community Edition is enough for Android Development
Disadvantages:
- less popular