I have to design something like that:
Should I use a Grid (2 rows, 2 columns), or should I use a horizontal StackPanel with button 1 and another vertical StackPanel with buttons 2 and 3.
And especially - WHY should I use each option.
You should consider your layout panel based on the following contexts:
Moving, Alignment, Resizing, and Docking.
If you use a WrapPanel
for example, you will notice that when resizing the window, the button's will maintain their original size and stack on top of each other to fit to the window size, while in a Grid
they will change their size to maintain their current location.
I suggest you to test your options by the mentioned ciritia's and choose what best fits your requierments.