The first looks like an event-handler, i.e. where you've used

this.Paint += OnPaint; // or the longer form

This might be useful for providing additional painting to components
outside of your control; however, for painting your *own* control, the
"override" approach is recommended; this allows more control of *when*
your painting happens (in relation to the background painting from the
base class, and any derived classes) - for instance you might chooes
not to even call the "base.OnPaint()". It is also marginally quicker,
but not enough to get excited about.

Marc