What is Best Event Handler to Dispose of Unmanaged Objects?

It depends on where they are declared, at what scope, and the way you use them.

The best place to dispose of objects is usually as soon as you do not need them anymore.

And for Unmanaged objects, you do not really dispose of them, you release them, often with the ReleaseComObject method.

OK thanks. The objects are created at Form_Load and used until form is closed.

Sorry I meant to say "managed" not "unmanaged"

If they need disposing then there is an overridable method called Dispose on every form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

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add your code in there as required

These are database objects and are used potentially till form is closed. Therefore I will place in Form_Closing Event handler. Previously most were in Form_Closed. Thank you.