Custom vs User control

Choice is not only between user control and custom control, but among user control, custom control, customizing control template, customizing data template, header template (for collection based controls), attached properties.Refer to Control Authoring overview

I go by following order of consideration

1. Attached Properties : If functionality can be achieved, I use attached properties. Example, Numeric text box.

2. Control Template : When requirement can be fulfilled by customizing the control template, I use this. Example, circular progress bar.

3. Custom control: If control template cannot do it, I use custom control. Provided I need to customize/extend already present control. Example providing Sorting, Filtering based on header row in GridView (GridView is present in metro apps, used just to illustrate the example)

4. User control: Least preferred one. Only when composition is required, and I am unable to do it using custom control. Like in your example, 2 Combobox, and 1 datagrid. User controls does not provide seamless lookless feature that can be leveraged through custom control or control template.

You already have some great answers that explain the differences but also understand that custom controls and UserControls have different purposes:

A UserControl typically encapusulates some sort of composite behaviour. If you have an application that needs to edit contact details in many places, for example, you could create a custom control that has the labels and text fields for all the data laid out with a submit button that has the relevant code and reuse this control throughout your application.

A custom control is a control that is derived from one of the WPF control classes (E.G. Control, ContentControl etc.) and has to be created in code. These control usually have a single cohesive purpose (think TextBox, ComboBox, Label) rather than acting together as a whole (although this doesn't have to be the case).

UserControl's are usually easier for people unfamiliar with WPF as they can be visually designed.

My suggestion would be to start off with a UserControl. You can always refactor this into a custom control at a later date as you become more familiar with the way WPF works. Creating your control as a custom control will require knowledge of ControlTemplates and Styles as you will need to provide your own to define a look and feel for your control.

When all is said and done, as long as the control behaves correctly, it doesn't matter which approach you use.

See this post for an example of two approaches to the same problem. The post author wanted a control which can present modal content in front of the primary content. The post author actually answered his own question by implementing it as a UserControl. I have added an answer to the post which creates the control as a custom control but both have the same end effect.

• If you have a view-model and you wish to create a view for it use the User-Control.

• If you need an autonomous control that has no specific view-model,
  you probably need a custom-control.

• If you find that the functionality you need as whole, already exist in other controls you need to override an existing control template.
  (i.e: for a diamond shaped button - you need to override the button control template.)

• Regarding attached-properties and attached-behaviors, those are useful when you have a control which you want to extend with more properties or you want it to behave slightly different than its default behavior.

In the provided case of the composition the OP described, it can be achieved with either user control or custom control. I would prefer a custom control since there is no specific view model provided, the "input" is only a property bound to an item collection.

Oh, and, I am sorry for slightly being late.