There are different displays that are used in the gadgets and electronics that we are using right now. Retina displays make use of LCD while Amoled will make use of LED. For this reason alone, you can already guess that people will make a choice based on this alone.
Super Retina display will usually have a higher resolution as compared to the AMOLED display. You can expect that the viewing angles of the Amoled will be better than the retina, especially when you are exposed to sunlight.
Amoled can be harder to produce as compared to Retina, which also explains why they are sometimes priced higher as compared to Retina. There are still other factors that will change their prices.