I think it is better to say about the frameworks versions in addition to VS versions. Sure newer Framework is better because it has more functionality however the newest framework may be not compatible with ePDM/SolidWorks version. I'm using VS 2008 with Framework 3.5 or 2 and have never experienced the problems.
What about Express version. You can easily use it however be aware of limitation of this version: so far I know that it is not possible to setup the build actions and debugging process to start and attach through the UI in VS Express.
Artem Taturevych, Application Engineer at Intercad (Australia)
translationXpert – add-in to translate SolidWorks models
Using Visual Studio Express 2012 & .NET 4.0 with EPDM 2013 and it works great. I can debug line by line by attaching my DLL to the explorer.exe process.
Make sure your add-in is loaded (through admin tool) and active (right click a file to initiate the re-load) before attaching to the process or you may have debug symbol problems not loading, and break points not being hit.
If I have a lot of updates, I remove the add-in using the admin tool, and add it in with the debug option. That works great when I need to recompile multiple times. Simply end the explorer.exe task and re-start it between compiles and navigate to a file in the vault and right click it (to activate the add-in) and re-attach your DLL to the explorer.exe process.