I realize that there have been similar questions, but they seem to have been from when Qt Creator was still in beta, so the answer might have changed since then:
We are going to start a project with a small amount of GUI that needs to work on Windows, OS X and Linux. So choosing Qt was a no-brainer, even though we have little experience with Qt.
What is currently the best option for IDE?
All the developers will be using Windows machines, so the IDE does not need to be cross-platform.
We use Visual Studio for most things, but most of us are also comfortable with Eclipse.
How are the refactoring tools in Qt Creator? I like Visual Assist X when using Visual Studio for C++. Have anyone tried using that with Qt-projects?
I realize that was a lot of different questions. Please answer even if you can't answer all of them.
EDIT:
I should probable add that we already have Visual Studio and Visual Assist licenses, so the cost of those is not an issue.
I use Visual C++ 2008 with Visual Assist and Qt Creator with MinGW:
QtCreator is a good alternative to VC++ and I would definitely use it on Linux. If you already have VC++ 2005 or 2008 and VA X, I recommend that you install the Qt addin and use VC++ for development. I also recommend that you install the Qt SDK side by side and compile in both MinGW and VC++ to catch cross-platforms issues early! Try to keep the .pro files in sync to the sln and beware of this issue.