Obviously, will depend on what you want to use the rifle FOR.
If your shots are typically at 200 yds, then the 2 MOA dot covers 4 inches, the 4MOA 8 inches. Human face is about 8 inches across.
Extend that to 500 yds- the 2 MOA dot covers 10 inches wide, the 4 MOA 20 inches wide. A bit bigger than the human body.
600 yds- get a scope.
If your purpose is quick target acquisition inside of 200 yds, I'd go with the 4, over that, the 2. However, that is just my opinion. Anyone else? Anyone? Bueller?