I want to write a visual studio addon to do some code modifications for me (like some specific refactoring). I was wondering which one of these tools should I use and why?
we have licenses for resharper, the other two are free and this is an internally used software, so we don't need to worry about licensing.
If you've figured out the ReSharper API sufficiently to do useful work with it, then you should sell your knowledge to the highest bidder. They've been promising documentation for the past three major releases.
Although I have looked at ReSharper I have not used it much. I have used DXCore and I like what they have done. VSX looks promising especially with MEF in VS2010.
If you were going for a more general audience I would say VSX. But since this is internal to your organization I would go with DXCore.
More DXCore info here.
I have only used the DXCore but I have to say that it totally rocks.
My self and other developers have achieved a lot with this very capable framework
I submit our community site as evidence to this effect.
DevExpress are very helpful when it comes to answering questions on particular uses of the framework and in many cases, enhancing it to provide additional functionality for those who write plugins based on it.
I have written quite a bit on the creation of such plugins on my blog and I am endeavouring to keep this page on the community site up to date with links to several pages around the internet containing tutorials and fully worked examples.
I also intend to continue writing tutorials on the topic on my blog, so this should become an even better resource over time.
Refactorings are extremely easy to write with the DXCore, because of it's extremely comprehensive object model.
I am also happy to answer questions on the topic of DXCore (and Coderush/RefactorPro) via http://twitter.com/RoryBecker or alternatively via email (Rory Becker at G Mail dot Com)
I suggest you use the framework you're most familiar with its API. If you need to do something complicated (i.e parse code, eye candy effects) you do not want to use VSX - it would take too much time.
In case you don't have a preference I suggest you'll use DXCore mainly because its API can be quickly learnt, although there is much to improve documention-wise you have a few example projects as well as a very supportive community. Whenever I've needed to discover how to do something, all I needed to do is ask about it at the DXcore plugins forum and I got my question answered in a flash.