Which IDE Do you use for Building Flex Applications?

This question comes in from a long time development friend, Aaron:

What I was wondering on is what version of the Flash Builder do you use and why? I see a premium and basic versions, in regards to the premium I am not so sure I care about [the extra features]

I use Flash Builder 4 Premium, mainly because it is easily available to me since DotComIt is a member of the Adobe Partner Program.

That said, in the course of my normal development I don't use any Premium specific features. The premium features are the profiler, the network monitor, and unit testing integration. ( And CF Builder is included with Premium ).

In terms of the Network Monitor, I use ServiceCapture if I need it. It works great, and is already a tool in my set. I have no need to change.

With regards to Unit Testing integration, I I was never able to get it to work during the prerelease cycle and eventually gave up. When I need unit testing, such as building components for Flextras, I create an AIR project and use FlexUnit.

The Profiler is more interesting, though. It is used for performance tuning; which is important in many enterprise class applications. However, I've not had much experience with it.

There are also some alternate IDEs out there including FDT and IntelliJ as well as some Visual Studio plugins. I haven't explored any of them in depth, but I've heard good things about many of them.