For shooting birds (skeet, upland, waterfowl), I find that bead sights are best. They also offer reasonable accuracy with slugs, out to about 25-50 yds.
For longer-range slug shots (50-100 yds), ghost ring or open iron sights offer more precision. However I find that these are a bit slower and less accurate for wing shooting, because they are higher than bead sights and don't give the same cheek weld (unless the comb of your stock has been raised accordingly).