I think Panel in VB.NET is basically what PictureBox was in VB6... I mean
who really used them to display pictures? They were used as drawing
surfaces, control containers, and buttons, but rarely was the PictureBox
used over the Image control to display pictures.
In VB.NET, the Panel, I believe, is what you use for a control container
and whatnot, while the PictureBox is for displaying images (note the
lack of an Image control). I'm not 100% sure which you should use
for drawing on (when you're not using the form) in the case of a
painting program or whatever, but I would assume the PictureBox.
It probably doesn't matter much though.