Q: What are the differences between the portable and setup version?
A: The only difference is that the portable version ships with an executable called "devcppPortable.exe" which tells Dev-C++ to store its configuration files in ".\config\" instead of in %APPDATA%. Dev-C++ will be executed the following way:
devcpp.exe -c .\config <parameters passed to devcppPortable>
As a result of this, the Dev-C++ folder can be moved around and Dev-C++ will keep working.

Q: Q: What are the differences between the 32bit and 64bit version?
A: The only difference is that the compiler that ships with the 64bit version can create 64bit programs. All versions work on 32bit systems. When using the 64bit version on 32bit systems, please make sure to compile for 32bit, or you won't be able to run your compiled programs. Check out the section to find out how to do that.