From a theoretical point of view, the effectiveness of dihedral is more the further towards the tip you are, leverage and all. So for most effect with least dihedral a eliptical dihedral is ideal. But darned hard to make for the added benefit.
Single break comes furthest from the ideal, but is certainly easy to make.
Double break is only slightly harder and approximates the eliptical form. I also find it easier to make because I have the flat center section to reference when I'm adding wing posts, adjusting wash or checking wing settings.
Tip plates are an extreme form of double break. They're also trying to minimize something called tip vortices. You can see tip vortices in photos of large jets taking off and landing through a cloud of steam or dust, but they are there all the time, and a major contributor to the drag caused by a wing. Many modern jets have tips jutting at odd angles just to control this. I'm not convinced they have much effect on tip vortices in our designs, but they are easy to make, and fly well. One caution though, you have to make sure you are dead accurate in building the tips to make sure you don't get a snow-plow effect greatly adding to the drag instead of improving it.