The main difference between User Control, Custom Control and Component is that they inherit from different levels in the inheritance tree:
MyComponent
|-> Component
MyCustomControl
|-> Control
|-> Component
MyUserControl
|-> ContainerControl
|-> ScrollableControl
|-> Control
|-> Component
So, in short you get a different amount of pre-wired functionality with the different options.
When would you use the different options? (these are thoughts and opinions, not truths)
- Create a component if you want to provide functionality without UI (such as Timer components, data sources, …)
- Create a custom control if you want to make a component where you have full control over its visual appearance, and you don’t want any baggage of unnecessary functionality. Typical cases would be simple controls with limited functionality (such as a button)
- Create a user control if you are going to combine existing controls into reusable building blocks (such as two lists with buttons where you can move items between the lists).