Win32 and AA spy modes use different engines to find and match against a set of interface elements in the user environment. They use different attribute sets and matching methods to determine which elements to interact with.
I feel that the Win32 spy mode tends to be faster and more reliable, but Active Accessibility is compatible with more types of interface elements. When automating Windows-native applications, Active Accessibility should only be used when elements are not compatible.
You can find more information about the attributes each spy mode returns to the Application Modeler in Blue Prism built-in page and Blue Prism Foundation Training guide