Taking into account that a user control is a user control regardless of the framework then Ralf is correct. The question you're asking should be:
"What is the difference between Windows Forms and WPF ?"
Read the following from Infragistics...
Windows Presentation Foundation vs WinForms - Evangelism - Infragistics.com Blog[
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It covers the question in more detail but the first paragraph sums it up nicely:
WinForms provides access to the native Microsoft Windows interface elements by wrapping the existing Windows API in managed code. WPF on the other hand, is the new platform for Microsoft Windows application development, based on the .NET Framework. This framework provides a clear, object-oriented, extensible set of classes that enable you to develop rich Windows applications.