I don't think you can compare them because fundamentally they are so different--VB6 controls versus .net framework controls that is.
Take a look at the class hierarchy in .net and you will see that both picturebox and label derive from the same set of classes.
While I didn't itemize the classes' properties and methods, I would guess that the only difference between a Label and a Picturebox is that there is a text property for a Label box thus alleviating you of rendering your own text if there were no Label control and all you had was a PictureBox.
Both a Label and a PictureBox can be assigned an Image object or work in conjunction with an ImageList. So if all you are looking to do is display images then the PictureBox should be just fine (not to mention the fact that it clearly conveys the control's purpose in life: PictureBox:Icons::Label:Text).