Depends on the competition. Those big dots can be picked up fast, but take longer to be precise with. It's all a trade off. My preference for outdoor shooting is Dawson black rear, red fiber front.I have iron rear sights with an XS Big Dot front I pick it up great. What I want to know is why so many who shoot competitions prefer the fiber optic fronts?
FO's are designed to simply pick the front sight up faster. Unless you use an adjustable rear there really isn't a way to adjust POA/POI zero'ed on the FO. That why I like the TARAN's so much better than the DAWSON's The FO is alot closer to the top of the sight.FO fronts are easier to use for coarse sight pictures, when the FS does not need to be indexed precisely. For tighter shots, the top of the FS is a much better indexing tool.
The dot and post are 2 separate points of index. It doesn't really make sense to zero a gun with irons so that it prints at the dot.