Form.Invalidate(...)

Does anyone have any idea which of these is more efficient?

Code:

---

List<Rectangle> rectangles;
//some code to build the list (up to 56 rectangles)

// (1) is this the quickest?
foreach (Rectangle rect in rectangles)
  this.Invalidate(rect);

// (2) or is this?
Region region = new Region();

foreach (Rectangle rect in rectangles)
  region.Union(rect);

this.Invalidate(region);

---

OR... is it dependent on too many other factors to make a judgement?

Incidentally, in my scenario, if I use the region (2) option, then I don't need to build the list of rectangles beforehand, I can just add them to the region as they are created. This is because either the List<Rectangle> or the Region is returned from another function and not actually created in the same routine as in my example above.

Test test test, that is the best way to determine these things. however, If I had to guess, I would assume that option A would be quickest due to the simplicity of handling rectangles as opposed to amorphous regions. Maintaining a collection of rectangles is trivial.