How do I decide whether to use ATL, MFC, Win32 or CLR for a new C++ project?

http://stackoverflow.com/questions/821676/how-do-i-decide-whether-to-use-atl-mfc-win32-or-clr-for-a-new-c-project

It depends on your needs.
Using the CLR will provide you with the most expressive set of libraries (the entire .NET framework), at the cost of restricting your executable to requiring the .NET framework to be installed at runtime, as well as limiting you to the Windows platform (however, all 4 listed technologies are windows only, so the platform limitation is probably the least troublesome).
However, CLR requires you to use the C++/CLI extensions to the C++ language, so you'll, in essense, need to learn some extra language features in order to use this. Doing so gives you many "extras," such as access to the .net libraries, full garbage collection, etc.
ATL & MFC are somewhat trickier to decide between. I'd refer you to MSDN's page for choosing in order to decide between them. The nice thing about ATL/MFC is that you don't need the .NET framework, only the VC/MFC runtimes to be installed for deployment.
Using Win32 directly provides the smallest executables, with the fewest dependencies, but is more work to write. You have the least amount of helper libraries, so you're writing more of the code.