I can't believe no one has mentioned XCODE yet.
I've used over a dozen different IDE and none have come close to matching XCODE's features and usability.
Granted, xcode does have some drawbacks, but the benefits far outweigh the limitations.
So, as a full time iOS developer dating back to Xcode 3, and someone who has professionally developed for android on both eclipse and android studio, I do prefer Xcode to both of those, but its not because of its features or usability.
Feature wise, I think Xcode is pretty limited (for objective-c/cocoa development):
It's code formatting settings are pretty basic. Our coding standards can't be achieved 100% through automatic settings.
You can't edit the default code snippets without using a 3rd party app to do it.
Refactoring is slow, because you have to let it show you the diff and doesn't make changes inline.
You can't even do things like remove unneeded imports. Sorting things alphabetically requires 3rd party scripts.
Xcode updates tend to introduce new issues and crashing.
Xcode doesn't do basic things like automatically stubbing out required protocol methods.
These are just some of the issues I could think of off the top of my head, but there are many more. One thing I really really like about Xcode/ios is that the instrumentation for things like profiling and debugging weird issues sooooo much better. Ever try and debug object retention issues on Android? How about memory issues in the native layer? How about just profiling an app in general? The tools are awful.
The biggest reason I like Xcode is that it's native to the OS it runs on. Android Studio (and AppCode by the same people for iOS) and Eclipse are java apps, and I am really really picky about UI look/feel and behavioral consistency with the greater system.
xcode has come a long way though. Version 3 had a lot of features but the UI was a mess/confusing. Version 4 took away features but revamped the UI. Version 5 has refined the UI and added some features back.
Looking forward to version 6.