AutomationProperties.Name VS x:Name

Summary

x:Name and AutomationProperties.Name are two totally different things, so the question "should I use one or the other" is based on a false premise: in general, you cannot use one or the other.

The purpose of x:Name is to identify a WPF control in code-behind so that the developer can access it. It is not meaningful (or unique) outside the scope of the class that models a specific WPF element.

On the other hand, the purpose of AutomationProperties.Name is to identify a user interface element in the context of a dialog or other type of window that is presented to the user for interaction. Specifically, its value should match what a user would perceive as the "label" of that user interface element (so that e.g. an accessibility tool can inform the user of the purpose of the element).

While any tool (such as a XAML compiler) can choose to use the value of x:Name for AutomationProperties.Name as well doesn't mean that it's something you should do; IMHO this is exactly the type of "convenience" that results in problems because the difference between the two is hidden from the developer, so invariably one or the other property would end up having a semantically wrong value.

Information on the semantic and technical aspects of each of the property follows in the next sections.

x:Name

The MSDN documentation page explains that

After x:Name is applied to a framework's backing programming model, the name is equivalent to the variable that holds an object reference or an instance as returned by a constructor.

The value of an x:Name directive usage must be unique within a XAML namescope.

[...]

Under the standard build configuration for a WPF application that uses XAML, partial classes, and code-behind, the specified x:Name becomes the name of a field that is created in the underlying code when XAML is processed by a markup compilation build task, and that field holds a reference to the object.

From the above we can tell that x:Name:

1. is used to access the element in code (not XAML), since it controls the name of the field that holds the element
2. must be unique within a XAML namescope (since you cannot have two fields with the same name in code)

AutomationProperties.Name

The WPF accessibility documentation explains that

The Name for an automation element is assigned by the developer. The Name property should always be consistent with the label text on screen. For example, the Name must be “Browse…” for the button element with “Browse…” as the label.