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.
qtcreator with ccache and make -j 5 make compile time cut down to almost unnoticeable.
I was confronted with the same problem not so long ago. I chose QtCreator in the end, because it really grew stable over the past few months.
It's just so much easier to have all your tools within one environment. The debugging facilities are also quite extensive and integrate well with the Qt framework. Code completion is almost as good as in Visual Studio (as long as you don't own Visual Assist ;-), and the code navigation is very easy to use!
That together with the fact that QtCreator works on all three major platforms made the difference for me in the end.
I think when starting a new project, QtCreator has become a serious alternative to consider...
QTCreator is still in the beginning of its dev if you are facing it with Visual Studio.
Personally I'm using QTCreator for QT devs since all QT environment (IDE, QTDesigner, QT Documentation) is embedded and I find it great but not mature for now.
But since you used to develop with Visual Studio (with the Visual Assist X add-in) you should continue using it. In addition new QT binaries have been released for Visual Studio 2008. So no need to compile QT before using it!
Edit (Oct 5) : Next QtCreator release 1.3 will have an improved completion system at least as good as Visual Assist X : http://www.youtube.com/watch?v=TyfO-7lvy%5Fc&feature=player%5Fembedded.
Hit CTRL+K in QtCreator.
I would recommend to at least try QtCreator. Obviously for someone used to Visual Studio the transition won't be overnight but in the end I believe it'll be worth it.
Main reason is although you mention all developers will be using Windows, eventually you will have to run the program on other platforms during testing. And then it's hard to imagine you won't need to debug and fix things. You can do just fine with gdb/vim but for someone who's used to a debugger/editor experience that Visual Studio delivers, getting used to gdb/vim can take some time. QtCreator isn't perfect in this area, but it's as close as it gets to Visual Studio.
A few other points worth mentioning:
Another possibility is using Netbeans. Have a look at this
Netbeans provides great tools about memory and profiling for free. Morevover, the integration with Qt is nice.